1. We will go to school by bicycle along the coast road.
2. We will go to school by bicycle along the coastal road.
(Do we have to use 'coast' or 'costal"?)
3. He took the bus.
4. He get on the bus.
5. He used the bus.
6. He rode the bus.
(Can we use all the four expression? Which ones are the same?)
Either the coast road or the coastal road is correct. Both mean the same: a road that runs along the coast.
Unless #4 is a typo, and you mean he got on the bus, all four (3-6) are correct.