I'm a TA in a secondary school and really enjoy my job most days. I was previously a nurse in mental health and gave up my registration for health reasons.
I work for 28 periods a week with numerous children and about 15 different teachers. Most teachers are fine and friendly, some aren't so good at helping to direct you. In some classes I am expected to co-teach. discipline and mark as I go, in others I will sit with one or two children and help them to complete the task as well as they can.
Some teachers pretend I'm invisible, others include me in discussions and ask my opinion and use my life experiences as examples. Teacher's are as varied in their approaches as the children are!
When I'm invisible, I just tend to watch for where the disruption is happening and place myself nearby, or next to, the child who is making the most noise. Distraction and praise can work very well, and humour always helps.
When the teacher includes me then I'm happy to circulate and get involved with the discussion. If I can help with figuring out to answer questions in tasks, then I will but sometimes I'm better at helping them to find their own notes and working it out from there. It's difficult to know enough about all the subjects, especially if we don't follow the same class in every period that they're with that teacher.
Often, if the teacher is young or struggling, I'll approach and offer to take the child out or work with them on something different. When the child has SEN, many teachers aren't confident in how to deal with them and rely on you intervening.
You have to be very adaptable as you might be asked to do lots of different tasks in a day. In primary you can jump from reading with a child to first-aid to breaking up fights in the playground. A lot of your skills will come with experience and you'll soon appreciate the good TAs when you see how they approach challenging situations with calmness and pragmatism.
Good luck!