Normally when you quit less, your screen will be redrawn and you will be back with the content you could see on your screen before using less. Sometimes though it’s very handy to see the file with less, scroll down to the fragment of your interest and have that fragment still visible on the screen after you quit less.
Although the results may vary depending on what kind of terminal you use, try -X option when invoking less:

less -X /path/to/file

This and more cool tricks with less can be found on the excellent less FAQ.