I would like to log in an application with multiple users(each of who has an active session when logged in) and do stuff. Instead of logging them in, one by one in seperate thread groups, would it be possible to load e.g. 20 users from a CSV file(with each having a unique session) in one thread group?
I log each user in a seperate thread group, yet i would like to automate things a bit more.
Sure, you can (actually you should — thats how Thread Group works) use one thread group to simulate concurrent users.
Set "Number of Threads (users)" to e.g. 20.
In addition you may read the Guide to JMeter Thread Groups to get more information.