How to save and restore multiple different sessions in Vim?

Depending on my task in Vim I have several tabs open.

How can I save different sessions for later use?

You want something like

:mksession ~/mysession.vim

Then later you can source that vim file and you'll have your old session back:

:source ~/mysession.vim

or open vim with the -S option:

$ vim -S ~/mysession.vim

You might want to set these session options in your vimrc. Especially options is annoying when you've changed your vimrc after you've saved the session.

set ssop-=options    " do not store global and local values in a session
set ssop-=folds      " do not store folds

Note that :mksession will not save the changes to any files that you've made. I made this mistake of closing vim after saving the session assuming that I'll take up from there. But next time I opened the session, the changes I had made to the files were gone.