A hotel is a place you stay while traveling or on vacation.
The word motel comes from "motor hotel" and is a hotel for motorists (drivers). They are usually found near highways, so you can stay there when you are driving a long distance and need to stop for the night. Motels usually have very basic facilities, and are less expensive than hotels. The doors to motel rooms are often on the outside.
Hostels have dormitory rooms with multiple beds, so you share the room with other travelers. Hostel rooms may have men only, women only, or they may be mixed - and some hostels do offer private rooms as well. A hostel is also typically less expensive than a hotel. Students and backpackers often stay in hostels.
Note the pronunciation difference in these words: hotel and motel have the o sound in the word "no," and the "o" in hostel sounds like "ah," like in the word "hot."