Clueless, can anyone help?

[makingmiracles]

So I am going back to work after 10yrs as Sahm and I wondered about tax, will I be put on an emergency tax code? If I am, do I need to ring hmrc or does it get adjusted automatically?
Also my gross earnings for the year will be 13,975, so only about 1500 above the personal tax allowance, how do they work this out, will I still be taxed on earnings at 20% from day one? Then rebated next April?

Just trying to get my head around it all!