Here's a simple (unix) example that zips two files in parallel:
systask command "gzip /user/home/andy/alpha.csv" nowait taskname=alpha;
systask command "gzip /user/home/andy/alpha.csv" nowait taskname=beta;
waitfor _all_ alpha beta;
%put Both files are now zipped;
Note the NOWAIT keyword on each SYSTASK statement; this instructs SAS to continue execution rather than waiting for the command to finish. The WAITFOR statement (as its name implies) forms a synchronisation point in your code. In the example above, it will wait for "all" of the tasks named on the WAITFOR statement before allowing execution to continue beyond the WAITFOR statement.
In SAS 9.1 there's a restriction whereby you cannot use a tilde (~) or a wildcard (*). Aside from that, SYSTASK is a terrific means of speeding-up your SAS code and making greater use of your computing resources.