To "rely" on something or someone is to have trust in that thing or that person. It’s very similar to the word "depend." When used as a verb, "rely" is almost always followed by the preposition "on."
You can rely on Bill. He’s a very good worker and he always finishes things on time.
Can we rely on Francine to get the job done?
They can’t rely on Jeff anymore. He’s not a very responsible person.
Helen relies on her car to get her to work every morning.
Who do you rely on for help?
We rely on our local grocery store for fresh produce.
You can rely on Alice to do a good job at work.
The word "reliable" is the adjective form of "rely."
Ralph is a very reliable employee. He never misses a day of work.
You need a reliable means of transportation to get to school every day.
Sandra relies on her cell phone for many different things–not just making phone calls.
You can rely on Alice to do a good job at work.