Roaming to other lanes to get kills is a legitimate thing in actual games, and if you can push up the lane in order to be able to roam and get kills, then it's often something you should be doing. It's a lot more difficult in real games versus players of course as they'll push back and will be trying to kill you and/or take tower, plus kills are somewhat rarer compared to bots so unless someone roamed, there probably wouldn't be a kill to be had at all. (And remember, you do get gold/xp for kill assists too, so not personally getting the kill isn't a huge deal as you'll still be getting an advantage over your lane opponent, both in terms of the immediate xp/gold, and from the time you can then spend farming before they can get back to lane.) Seeing how they get the kills is also potentially insightful regarding where they position themselves, when they'll chase and when they'll back off, when they'll use abilities and what they'll save, etc.
As for them taking all the minions, what is it that allows them to steal all the minions, and what aren't you doing that yourself? The only difference between their csing potential and yours is a handful of runes/masteries, and 99% of the time if you're csing properly then that won't make a difference, so watch what they do to clear the wave(s) effectively.
Experience, as in the stuff from the 1-30 leveling system, is independent of your performance in the game and only on game length, if it's win/lose, as well as the type of queue (bots being poor for xp compared to pvp). Kills don't influence your xp at all. (Incidentally, I think winning a ton of as-short-as-possible games is actually more efficient xp than a handful of hour long marathon games, even though you'll get more xp per game in the latter case, the base xp you get makes the short but high volume approach make up for it.)
Remember that PvP games matchmake you with similar leveled/mmr people, and you're high enough level that you're sortof shooting yourself in the foot if you don't 'force' yourself to play PvP. Level 1-20 or so (probably less) real new players are understandably apprehensive about playing PvP since they feel like they don't know the game and they'll get stomped. They would in theory get matched with other people the same level as them, and it's quite common for people to be all "this is my first pvp game, sorry in advance" to get responses along the lines of "Don't worry it's my first PvP game too", and it can be actually somewhat fair game (if perhaps a perpetual facepalm experience to any spectating veterans). In practice there's probably random smurf accounts mixed in in that level range since they're the ones who aren't afraid of PvP games despite being low level, but if you lose a handful of games you'll be 'under' the smurfs mmr wise and get truly fair match ups (as in people who don't know the game versus people who don't really know the game).
Levels 20-30 though people who are legitimately new often start braving PvP. It's less smurf infested by that point, as the smurfs generally started earlier and have significantly higher mmrs by the time they're in their 20s levelwise, but you'll still bump into the occasional one who'll trash you, but often times it's people who've mostly played just bots up until that point, so relatively fair. It'll be frustrating to both sides as they discover that almost everything they learned from bots doesn't work anymore, but it'll be a fair first step towards learning how to play.
By the time people are freshly level 30, most players will have dozens if not hundreds of PvP games under their belt. If you manage to make it to 30 via only bot games, when you do go to pvp, you'll almost certainly get stomped. It probably won't even be because you get matched with some super pro smurf or gold+ ranked veteran, it'll be players who legitimately just got to level 30 on their first account, but who actually learned the game via playing PvP pre-30 when the game 'expected' them to. And then you'll play some more games and get stomped more, and that'll repeat for awhile until you either get frustrated and quit, get frustrated and return to bots (and then get bored and quit), or your mmr drops low enough that you're matched with similar bots-only people and trolls who dropped there not due to lack of game knowledge, but rather their active desire to make others miserable. These are not good options, which is why everyone has been urging you to avoid playing bots. It's not trying to pick on you, it's genuinely trying to set you up for success.
Trying to learn the game by playing bots is like trying to learn chess by playing checkers. You'll learn the most rudimentary things (theres a grid, theres pieces on the grid, there are rules about how the pieces move), but you can hardly be said to have learned chess. Even if you become a top tier checkers player, if you try to play chess against even an awful chess player, you'd lose, since they still know how to play. The things you can reasonably learn from bots is the layout of summoners rift, that there are champions, they have abilties that do things that you can activate with QWER, getting the last hit on minions gives gold, and towers shoot you unless theres minions around and they hurt. You don't need other players to cooperate with you to grok any of that stuff, you just sortof need to get in there and play around with the buttons a bit.
Even something like csing you won't really be able to learn effectively in bots, since bots offer unrealistic amounts of harass/waveclear of their own, which will completely alter how one last hits in a 'real' environment.
