Learn Russian: Шрифт выбирается дизайнером.

This is how Russian expresses the agent (the "doer" of the action) in a passive sentence. In English, we use "by" (by the designer). In Russian, you simply put the noun in the Instrumental case: дизайнером.

Why does выбирается have the reflexive -ся ending?

Adding -ся is the standard way to form the passive voice for imperfective verbs in Russian. While выбирает means "chooses", adding -ся changes the meaning to "is chosen". The subject of the sentence becomes Шрифт (the font).

Could I just say Дизайнер выбирает шрифт instead?

Yes, absolutely! That is the active voice equivalent. Using the passive Шрифт выбирается дизайнером just shifts the focus onto the font as the main topic of the sentence, which is common in formal or technical writing.

Can I use a perfective verb with -ся to say the font was chosen?

No, the -ся passive is almost exclusively used with imperfective verbs to describe ongoing or regular processes. To express a completed action in the passive voice (like "the font was chosen"), you would use a short passive participle instead, such as Шрифт был выбран.