Hello Emily
Basic information about licensing can be found at Documentation | SAP Support Portal. Especially the SAP System Measurement guide, describes the process and provides some information about the LAW transaction and what you are able to do with it.
I'm not sure what you mean by: "how many PC are using multible logon, rate or status?" Multiple logon is determined at the SAP Server, not at the client side. Also licensing normally is not determined by the fact of the number of multiple logins or number of PC's. But the number and type of active users.
The LAW (SLAW tcode) allows you to 'consolidate' all the users, and licensetypes of various SAP systems. Here you can also remove duplicates / group users who have the same identity.