As far as I know the only way to make SEM is to be a validator.  To become a Validator, you firstly need to be a Delegate (this burns 1000SEM to register).  Then people vote for the Validators from the delegates, with 1 SEM per vote (this locks your SEM votes, but you can unvote if you want your SEM back).  As the network grows so do the number of validators, up to the current max of 100 validators.  Some of these Validators act as pools, paying out to their supporting Voters with a share of the SEM they forge.

I hope this all makes sense so far?