to make a phone call to someone

She rang me up to say she couldn't come. 她打电话给我说不能来。

He rang up the office and asked to speak to the manager. 他打办公室的电话，要求跟经理通话。

to record the money that has been paid by a customer by pressing buttons on a cash register

I'm sorry, I rang up the wrong amount. 对不起，我输错钱数了。