Ok i sopose you have a Snapshoot site, and Master site, and i sopose you want to enter some data in Snapshot site, then replicate it to master, and vice-versa.
You need to create a updatable snapshot on Snapshot site. It depends what you actualy use, lets say you use Oracle Lite. So in Navigator you should drag a table from Master site to Snapshot folder in Snapshot site. Then on other side at Master site, you need to tell him what tables can be updated, so in Replication manager, click on Replicated Objects and click Add, select the same table you draged to Snapshot folder on Snapshot site. (you dont need snapshoot on Master site).
Now you should be able to enter some data in Snapshot site, then click on snapshot file, and click refresh.
I hope you understand now, i didnt want to go to much in detail, because this would turn to be a book