I keep seeing words such as 'soit' instead of 'est' in texts and I don't understand what it is and why it's there, could you explain?

You are in dangerous territory, you have reached a time where you have no choice but to learn about this dreaded rule. The Subjunctive. You'll be seeing a lot more of this is you choose to take French as an A level or beyond so learning the basics now willl help tremendously! Many teachers think that it's uneccessary to learn about it at GCSE level as it 'over complicates' things so tell you to just learn the words without knowing when or why they are used. However I couldn't disagree more- how are you meant to learn if you don't know why you're doing something?!

The Subjunctive is what we call a 'Mood', not a tense. It describes the change of a verb as a result of another part of the sentence. There are a few basic rules as to what would need to happen in the sentence in order to trigger the subjunctive, I'm going to explain the most common ones..

1) Influence or personal opinion regarding someone else's actions

eg- 'I want you to do the washing up' - Here, you are stating that you want someone to do soemthing, meaning you are influencung their actions. You will have probabaly been taught to say 'Je veux que tu fais la vaiselle', however this is not technically correct (yes, you've been lied to!!). The verb 'fais' would need to chnage to 'fasses', the subjunctive conjugation of the tu form of 'faire' - 'Je veux que tu fasses la vaiselle'. Learning these subjucntive conjugations is the same as learning the presnt tense, you just have to memorise.

2) Negative form of your own opinion

This one is pretty straight forward. Whenver you say something such as 'je ne pense pas', you need to use the subjunctive. We don't know why, it's just one fo those weird language things... 
eg- 'I don't think that it is true' ---> 'Je ne pense pas que ce soit vrai'

Instead of using 'c'est' to say 'it is', we use the subjunctive 'ce soit'. I wish there was more of an explantion to this but i've learnt it really is just soemthing you have to accept and learn!

There are a few other (slightly more complicated) rules about when to use the subjunctive but these are the only two that will be useful for your GCSE exams. If you know you'll be choosing french next year then I would more than happy to explain everything in more depth, if you have the patience for a very long lesson! For now though, here are the subjunctive conjugations for a couple of the most commonly used verbs for you to learn-

ETRE

Je SOIS, tu SOIS, il SOIT, nous SOYENS, vous SOYEZ, ils SOIENT

FAIRE

je FASSE, tu FASSES, il FASSES, nous FASSIONS, vous FASSIEZ ils FASSENT

AVOIR

j'AIE, tu AIES, il AIT, nous AYONS, vous AYEZ, ils AIENT