You've got a C2 level in Spanish but don't know when to use the subjunctive? Something's not adding up here.

:)

the use of subjunctive is one of the few complex points of Spanish grammar (not too complex by itself, but because it differs from other major languages, which use subjunctive far less frequently) so you will have no shortage of online resources, as already suggested.

The way I explain it to friends, so that they remember it easily is that subjunctive is used whenever the action is a wish, hypothesis, or otherwise uncertain, whereas indicative are for certainties or actions that definitely occur. One point of confusion is the conditional, which is an indicative tense, because if the condition happens, then the action is expected to complete (therefore certainty)

so, for example:

Quiero lo que tienes (i want what you have, indicative) vs.

Quiero lo que tengas (I want whatever you (may) have, subjunctive)

Sé que me quieres (I know you love me, indicative)

Espero que me quieras (i hope you love me, subjuntive)

Cuando soy feliz, me río (when I'm happy, I laugh, indicative because I'm expressing it as a certain thing)

Cuando sea feliz, me reiré (when I'm happy, I will laugh, subjunctive because it's a hypothesis... It implies that I'm not happy now, so the clause has to be in the future tense)

hope that helps you.

http://www.elsubjuntivo.com/

https://www.youtube.com/watch?v=mlK3ZgGFpTU