Learn Hardcore Japanese: deetayouryou, roominguryoukin, opusyonsaabisu wo kakuninsuru. - I check the data allowance, roaming charge, and optional service.

Breakdown of deetayouryou, roominguryoukin, opushonsaabisu o kakuninsuru.

Why is there only one を even though there are three things listed?

Because all three nouns are the direct objects of the same verb, Japanese usually puts を only once after the whole list.

So:

are all being acted on by 確認する.

This is more natural than repeating を after every item.

What does を do in this sentence?

を marks the direct object of the verb.

Here, the verb is 確認する meaning to check / confirm, so を shows what is being checked.

In this sentence, the things being checked are:

Why are there commas instead of something like and?

Japanese often uses 、 to list items without adding a separate word for and.

So データ容量、ローミング料金、オプションサービス is simply a list:

This style is very common in menus, instructions, labels, and short written statements.

You could also connect nouns in other ways, such as with と, but a comma list is very natural here.

Why is the verb 確認する at the end?