Expenses for nights on Agency work

Can someone put this lot in layman’s terms for thickos like me please?

From what’s been said in this topic;

Because I’m an agency driver, I have no fixed place of employment and am therefore eligable for 38-40 pence per mile (can’t fathom if I need recipts or not), a fiver per meal (under certain curcumstances) and expenses relating to my work - I presume that’s workwear, gloves, any p.p.e, pens, paper, diaries, possibly even a replacement digi-card if I need one.

Not too sure about work related courses, is that for self employed/plc etc or can I still get that as an agency driver on paye?

If it can be back-dated, could I use my timesheets (which detail who I worked for and when) and say “that’s the last six month’s worth for brakes at grantham which is 30miles from home - pay up!” or do you get a kind “bugger orff” without a reciept?

How do I apply for these expenses, including where to get the forms?