S’en aller is an interesting verb meaning to depart or to leave. It’s slightly different from aller on it’s own because it places more emphasis on the act of leaving.
You should also note that this verb is pronominal, so we need to make sure that aspect is included when we conjugate it, and it is one of the few cases where the pronoun (en) comes as part of the verb.
Interestingly, “en” really doesn’t mean much here, it’s just how this verb has evolved, but it is required and this aspect suggests the idea of leaving “from somewhere”, which is good to note as this verb can also take an object preceded by de: “Il s’en va de Paris” – “He is leaving (from somewhere) to go to Paris”. Although, it may still be preferable to say: “Il va partir à Paris”
With that bit of analysis out the way (basically it boils down to it is what it is) let’s look at how this might be conjugated. Well we need to conjugate aller as normal, we keep “en” in place and make sure we change the reflexive pronoun:
Je m’en vais – I am leaving
Tu t’en va – You are leaving (informal)
Il s’en va – He is leaving.
Vous vous en allez – You are leaving (plural/formal).
Nous nous en allons – We are leaving.
Ils s’en vont – They are leaving.
In the negative the reflexive pronoun and en come after ne:
Il ne s’en va pas – He is not leaving.
Ne t’en va pas ! – Don’t go!
As with all languages, verbs can take on different meanings depending on context and this verb can also take on the meaning of “to die”, and when placed in the imperative it means “Go away!”:
Ma grand-mère s’en est allé – My grandmother has left / My Grandmother has died.
Va-t’en ! – Go Away!