I used to swim in the river years ago.

Used to é usado para expressar um hábito do passado, somente no passado, seguido de um verbo no infinitivo.

I used to swim in the river years ago.
Did you use to swim in the river years ago?
I didn’t use to swim in the river years ago.

To be used to é usado para expressar um costume, no presente, passado e futuro, seguido de um verbo com terminação ing ou seguido de objeto direto.

He is used to working in the morning.
I am used to the noise of the industry.
Are they used to going to school by bus?
We aren’t used to the new teacher.