@Sakata Spend a great deal of time reviewing all the materials provided by the school. As has been noted, there are differences between degrees and diplomas. The most common diplomas are those awarded at high school graduations. If you are interested in a trade school, you are probably better off with a face-to-face class environment that allows direct hands-on work with a teacher who can check and guide you work toward your goal. Also, look for a school that provides career placement for when you complete the program.
If you are looking for a degree program, be sure the college/university is accredited regionally (international or national accreditation is sometimes a problem) so that your courses could be transferred to other school in the event you decide one term at the school is all you want to do. A great deal of time and money is lost when coursework does not transfer.
Regarding online learning, it is very hard work to take an online course. Unlike traditional classrooms, you have to participate fully all of the time to complete the courses successfully. You have to have strong discipline as well as have the ability and the desire to work on your own. You must have excellent reading, writing, and computer skills to keep up with the amount of work that is required.