Post questions?

I have read on posts in the codex manual but can’t find the answers. I’m new to blogging and wordpress and am wondering how many posts you can do in a row. I saw something in the settings/ writing about lines in the post with a number in there. Mine used to be 10 now says 15 what does this mean and how did it change itself? How to do you stop the posts and put the old ones in archives? How do I manage the posts so that they don’t go on and on? Will they stop on their own and I won’t be able to post? These are probably dumb questions, but I don’t know the answers and can’t find them.
Can someone enlighten me? Thanks for help.
Sonni