If you're asking how to maintain two independent copies of a database, and have the changes in one copy reflected in the other, and vice versa, it can prove to be difficult - without 3rd party applications/plug-ins. There's a company that might offer something that would work for you:
Much depends on how your separate users will work with the data and the structure of your database. If there is the slightest chance that two users might modify the same record, you have to build a system where this is identified and you can then see both copies of the record in a meaningful context so that you can select which version to keep or whether to edit one copy to merge changes from both.
You can do it, but it's not easy. You'll need a date field in each table where data is to be merged to record the date the record was last "synched". You'll ned an auto-enter date or timestamp field to record when the record was last modified. You'll need to be able to link the table in your travling copy to the same table in your main copy so that such problem records can be compared and dealt with before using import records to "sync" the file.
The more complex your table structure, the more copies you have to synch, the more hours someone will have to spend evaluating different versions of such changed records.