When and how do I use the subjunctive?

The subjunctive is used to express emotion, doubt, wishes and desires, impersonal phrases, recommendations and opinion. Essentially, if you aren't certain about something then you use the subjunctive. For example, if you wish something to happen, you can't be certain that it will happen and therefore the subjunctive is required. Likewise if you recommended yesterday that your friend did something, you weren't certain that he would follow your advice the the subjunctive is required again.
An easy way to remember is WEIRDO - because it is a weird thing after all!W-wishes and desiresE-emotionsI-impersonalR-reccomendation D-doubt or denialO-opinion
The subjunctive in the present tense is fairly simple to follow. If the verb ends in AR, you just pretend that it's and ER verb and conjugate it with the correct ER ending. Do the opposite for an ER or IR verb.
The past tense subjunctive is a little different but we can come back to this once we have secured your confidence using the present tense subjunctive. Let's go through WEIRDO and conjugate some examples together.