How do you take down turrets faster?

I'm a complete noob and I’ve only played blind pick against AI thus far. I always take the longest in any team I get put in and I don’t understand how others take them down with such ease. Everyone gets through the turrets in their lane in pretty much no time and they’re all already working on the nexus while I’m still not finished with the first turret. Not an overexaggeration, it is that bad. How do I get better at this? I’ll try to explain my issue the best I can and hopefully, it’ll make sense. I stand behind my minions, moving around and killing the first wave of the red ones. That’s done. I move under the turret and start working on it (before, I had barely any impact on them. Then I got familiar with items and began to use some bonus damage ones, so there’s that, at least), but when my minions die under it, I start getting pushed back by the red ones before mine spawn again. Now, the opponent is already running to me, pushing me back even farther (Gotta stay away from the red zones and all the opponents have those around them 80% of the time). When I manage to get this under control, kill the opponent or chase them away and get rid of the red minions, I can only spend a second under the turret before more red minions spawn, slaying the two blue ones left with me under the turret quickly. That happens after I only managed to give the turret two hits max. So I back away and spend another minute working on the new group of red minions. Some of them are standing directly under the turret. I can’t even go under it to fight a lot of them because the blue ones won’t go there unless there’s not a red one in sight. Then the opponent attacks me again, and repeat. I can only do this if I have somebody with me, but by myself, I’m embarrassingly useless. I can’t even get under the turret for more than three seconds at a time and for every millisecond spent beneath it, I spend a minute or two trying to get rid of opponent's minions outside of it, running and recalling because I'm low on health and struggling to keep up. It gets so overwhelming and messy. Any tips? I’m not really holding back, by the way. I throw all I have at the minions, but I only have the w avaliable that early into the game. Where am I messing up?