DHow to set number of posts to display on home screen.

This probsbly seems like a really dopey quations and I am a super n00b and very green so apologies.

However how do I determine how many of my posts appear on my homepage/front end?

I have migrated all my old blog posts over, and I only really want the last 4 or 5 to be on the front screen at any one time.

Sorry if I am missing osmething really obvious.

Thanks