"Assistance" means "help". "Provide" means "give". So "providing assistance" to someone means helping them.

One way that we use "provide assistance" is to talk about organizations that give money to groups to help people like disaster victims, people with disabilities, and so on:

Donations will go to provide assistance to families displaced by the recent earthquake.

You can also use "provide assistance" to describe helping someone in very formal speech. For example, if you are a witness in court, you might describe helping someone to the judge like this:

I saw a vehicle parked on the side of the road with its warning lights on, so I stopped to provide assistance.