How can I use “check out”?
Hi, when I look for check out in Macmillan dictionary, it says as follows:
2 [TRANSITIVE] AMERICAN to pay for your goods before leaving a supermarket or other large store

1. Then how can I use check out in this meaning? Could you please give me several examples?

2.
And I found this example: I'm about to check out—is there anything else you needed from the store?

Do you think it would be said by the clerk at the counter?

3. Can I use “check out” in the meaning of completing a payment as a clerk and a customer both? For example, can I say “would you like me to check you out now?” as a cashier at a shop?

Question

How can I use “check out”?
Hi, when I look for check out in Macmillan dictionary, it says as follows:
2 [TRANSITIVE] AMERICAN to pay for your goods before leaving a supermarket or other large store

1. Then how can I use check out in this meaning? Could you please give me several examples?

2. 
And I found this example: I'm about to check out—is there anything else you needed from the store?

Do you think it would be said by the clerk at the counter?

3. Can I use “check out” in the meaning of completing a payment as a clerk and a customer both? For example, can I say “would you like me to check you out now?” as a cashier at a shop?

Answer

1. I’m next in line at the check out counter and I’ll be checked out in a few minutes. 
The guy at the check out counter had me checked out very quickly. 
Customer to store clerk: Where can I get checked out? 
2. The person asking this is talking to someone else (perhaps on the phone.) A clerk might ask: Are you ready to check out!

Answer

I would suggest you have a look at the Oxford learner's dictionary. https://www.oxfordlearnersdictionaries.com/us/definition/english/check-out?q=check+out+

Answer

In answer to number 2, no, that would not be said by the clerk. That would be said by a customer who is on his or her mobile phone talking to someone who is at home. The customer would be asking a friend or family member if he or she should find something else before paying and leaving the shop.