The present subjuntive is in many cases used with clauses which follow que.
It is also used after subordinators such as antes de que, para que and others (below).
Some of these subordinators always require the subjunctive and others may or may not require it depending on the situation being described.
The subjunctive is always used when following clauses which are started using subordinators - used to introduce the subordinate clause.
|before ...||antes de que ...|
|I have to go before he comes||Tengo que ir antes de que venga|
|I need to buy it before I forget||Necesito comprarlo antes de que me olvide|
|in order that ...||... para que ...|
|I always do it so that he is happy||Siempre lo hago para que este contento|
|He tells us jokes to make us laugh||Nos dice chistes para que reamos|