Session variables and site security

I’m trying to understand session variables as I feel I never used them properly. In Dreamweaver I would use MM_Username a lot to filter tables and return data based on the user. MM_Username was the only thing I Ever used because I didn’t really know how it was set to begin with.

Is it possible to set more session variables based on a users login? and how do I correctly use these variables to filter my data inn wappler. Is it more appropriate to use the site security setting to filter and link data on my page? Do I filter my data on the page side or the server connect side?

I’m sorry, I’m guessing this is fundamental but I would rater learn to do this right from the start