Help with "Freezing a lane" and how I should do it.

I tend to have trouble freezing the lane in mid or top, but as the adc I find that if you auto a minion once or twice then wait for the last hit then the lane will freeze and you won't have your lane opponent pushing you all the way under tower

In order to freeze a lane you must have enemy minions stationary and a minion wave of your own present as well as incoming. You can easily take out the 3 melee minions but you want to leave the caster minions alone until you can last hit them. There are many videos on youtube explaining this strategy as well. By the time you are either attacking the casters or they are dead, your minion wave will have arrived and your position will not have changed much.

What they said about freezing the lane is perfect. I just wanted to add something that you've probably heard before but i'm gonna say it anyways, you shouldn't be following the wave past river unless you have it warded. If you're playing a champ with low mobility, it must be warded very well. You'd be surprised how many people complain about getting ganked over and over when they have zero vision. Once you have vision of the river/any other route someone can catch you out on, feel free to extend pretty far. Just keep an eye on the map while you push and be ready to peel at any second.

Freeze it anywhere from the middle to near your turret. All you need to do is wait for the minions to kill themselves and last hit them. Just don't attack them, then last hit. It's harder to freeze when the minion wave on the enemy's side is bigger, or vice versa, but eventually the wave will reset on it's own and you will be able to freeze better again.

There is very few things you can do to make the wave push toward your side to be exact. You can (when the lane momentum is nearly even) tank the enemy minions before they meet your minion. This way their reinforcement will come first. The only other reliable technique is to make your wave bounce on the enemy tower by pushing it. The longer the enemy minions stop to kill your wave the harder it gonna push back.

Once the wave momentum is in your favor however, there is 2 extra things you can do. First you can limit the damage to a minimum. This could include not even last hitting. Once the enemy minions have an advantage they tend to take more and more speed. It is said that by keeping 3 magi minions alive, you can last hit and just deal enough damage to cancel reliably that increase of speed. The other technique to keep the momentum in your favor is to tank the minions damage so they don't move forward (specialy just before your tower).

Hope it help a bit.