Once you have a client specification defined and the P4CLIENT variable set, the next step is to pull the files for that client down to your local machine. This is done with the p4 sync command, which instructs Perforce to synchronize the local files in your client with the repository. The first time it runs, it will download all of the files. Subsequent runs will only download files that have changed since the previous run. This allows you to stay in sync with others whom you might be working with.
Sync operations only work on files that the Perforce server knows has changed. If you change or delete a file locally without informing the server, doing a sync will not bring it back. However, doing a p4 sync -f will unconditionally sync all files, regardless of their state. This is useful for resolving problems where you think that your tree might be corrupt.
You can sync a subset of your tree or client by specifying a relative path to the sync command. For example, to only sync the ufs directory of the smpng project, you might do the following:
% cd projectroot/smpng % p4 sync src/sys/ufs/...
Specifying a local relative path works for many other p4 commands.