Learn French: Ce semestre, je suis présent sur le campus et j'y assiste à un cours. - This semester, I am present on the campus and I attend a lecture there.

In this sentence, y means "there". It replaces the location mentioned just before: sur le campus (on the campus). In French, y is used to avoid repeating a place introduced by prepositions like à, dans, en, or sur.

Why does y go right before assiste instead of at the end like in English?

In English, we put "there" at the end of the phrase ("I attend a lecture there"). But in French, the pronoun y must be placed directly before the conjugated verb it modifies. So it becomes j'y assiste (literally "I there attend").

Why is it written as j'y instead of je y?

The letter y acts as a vowel in French. Whenever je is followed by a word starting with a vowel sound, it drops its e and connects with an apostrophe to make pronunciation smoother.

Doesn't assister mean "to assist" or "to help"?

It looks like it, but assister (specifically assister à) is a classic "false friend". It actually means "to attend" an event, like a class, a meeting, or a concert. If you want to say "to help" in French, you would use the verb aider.