Directory/File permissions?

I’m somehow new to Linux - so my questions might sound “strange” (wants to try SuiteCRM for a small association)

It is installed on a VPS running Plesk Onyx (CentOS Linux 7.4). Looking in the file manager it says User: xx (system user of the account) and Group: psacln ‪(psacln and psaserv are actually linux groups created by Plesk and which are used for various services and files. For example parent-level directories that should not be shared between sites uses the psaserv group, and files inside of your site will use the psacln group.)

I want to set the right permissions for files and folders - but also to be sure that I do not provide more rights than nessecary.