first time pumping? help!

Niamh
Hi everyone I need a bit of help I'm going for a small operation in a few days and I will need to stay overnight in hospital,
I've been EBF now for 3 weeks so I bought a pump today so that my husband can feed  our son when I am away.
I don't even know how to do this? Should I pump after DS eats or before? I've no idea!