if both waves are in the center (lets call them wave 1) and you kill your oponents wave 1 in a way that makes it so your wave 1 attacks your opponents tower, then the enemies wave 2 attacks your wave 1 their wave 2 will be held back by your wave 1 but still be full hp. next after your wave 1 dies your wave 2 will meet their wave 2 (both waves full hp) on the enemies side of the lane. assuming you dont shove the wave your opponents wave 3 will reach your wave 2 before your wave 3 comes because both waves 2 are closer to your opponents minions spawn. this means while your opponents wave 2 and wave 3 are attacking your wave 2 your wave 3 is still moving towards the waves so your wave 2 will die faster and your enemy will have more minions/healthier minions making it push to you. (note that if you are less fed they can tank your wave instead of letting it crash and set up a freeze)
this is useful to
you will probably hear the term freeze tossed around a lot without knowing how to do it the first thing to know is that in general to freeze you need lane prio, it is unpractical to freeze while you are losing lane as the enemy can just walk up to break it. To freeze first wave needs to be pushing to you (you can make it bounce back to do this) also the enemy wave needs to have at least 3 minions left after your wave dies but 4 or more are preferable as when trading you can accidentally kill minions. it is also better if they are caster minions as melee minions occasionally will run under your tower breaking your freeze. after your wave is dead hold the last 4 minions by standing in front of them to stop them from running into tower ( you can run in and out of bushes so they attack you less and you lose less hp, the hp loss is why some high elo players always by refillable potions) when your wave comes stop tanking minions and just last hit. the 4 extra minions will stop your wave from pushing out. when your opponent walks up to take cs trade or kill him.
this is useful to
if an enemy freezes and you are more fed simply kill his minions. he will either tank them and you can just kill him or let them crash where they will bounce back to you. if you are less fed you must use your ranged ability, ping your jungle and explain to them in chat that you need their help to break the freeze or try to break it and risk getting traded/ dying. you can also try to roam mid, proxy or take jungle camps allthough in most cases doing these is troll