How to run two sessions at the same time?

that is,

if one session is already run then open another new session, then two sessions run compatibly together.

if no session run, then just create one new session.

my problem is to let two sessions run together without conflict troubles.

by the way, what is difference between solidworks application instances and sessions concepts

Any ideas! I come here to ask help because I know lots professionals here.

Thanks in advance!