Complete a lane

i need help understanding what a lane is.
I finished a pack in what i assumed would be lane 1, but nothing happened.
so i guess the idea i had for lane was wrong.

I think lane was all the training mission packs in one “column” (there are 3), so let’s say that you’ll complete all the starter mission packs from the left, then that objective should be completed. Later on all the mission packs will become “Wild”, so each will contain 7 random missions.

It’s very confusing and many new players are asking for that.