To use crutches move both together weightbearing with the bad knee and crutches together then move your good leg through, or to equal it. In the Uk you’re not allowed out until you are safe on crutches and also on stairs with crutches. To use stairs you use only one crutch and the and rail however you carry the other crutch like a T.
Please ask for professional help, and while you wait there are you tube videos. Please just make sure it’s from a trained physio and for TKR.
There’s a good one to start you off called Partial weightbearing on crutches by Gloucestershire NHS trust.
And another by bodyandmindphysiotherapy8142 as he shows the two stages of crutch use as you improve.
I loved my crutches and was on them 15m, with 3 ops. Now just a stick for safety on rough payments.
Keep us posted please,