Edb.log is the current log file. When a change is made to the database, it is written to the Edb.log file. When the Edb.log file is full of transactions, it is renamed to Edbxxxxx.log. (It starts at 00001 and continues to increment by using hexadecimal notation.) Because Active Directory uses circular logging, old log files are constantly deleted as soon as they have been written to the database. At any point in time, you will have the Edb.log file and maybe one or more Edbxxxxx.log files.
The Edb.chk file stores the database checkpoint, which identifies the point where the database engine has to replay the logs, generally at the time of recovery or initialization.
Res1.log and Res2.log are "placeholders," designed to reserve (in this case) the last 20 MB of disk space. This gives the log files sufficient room for a graceful shutdown if all other disk space is consumed.