There are 3 types of assistanships in Phd programs:
(Teaching Assistantship) This type of scholarship covers all your expenses and gives you a monthly pay, but in return wants you to teach classes. Generally, you are either expected to give lessons in one of the most basic classes of your field or be responsible for problem-solving, discussion or tutorial sessions. To receive this award one must be fluent in English. If your English is not sufficient, you may be asked to come early in the summer and take English lessons. In some schools, this award may be given to international students with insufficient English levelswhen they contribute as “Graders”.
A Teaching Assistanship is also a very desirable award because it gives you working experience. If you are consdiering an academic career this experience will be definetely of value to you. Some schools don’t have fellowships and only awards teaching assistanceships. Some give a fellowship scholarship in the first years and support you with teaching and research assistanships in the following years. Obtaining a fellowship scholarship for the first years is ideal.
(Research Assistantship) Is a scholarship which covers all your expenses, pays you a monthly salary and in return expects you to work with a teacher as a research assistant. This type of scholarship is not usually aawarded in the first years. You are expected to take a few classes in your field then begin your research. Some schools give a fellowship scholarship for the first years then change this to a research assistanship.
(Graduate Assistantship) also covers your expenses, gives you a monthly salary and in return expects you to help a teacher in another way than teaching and research. Some schools make these kinds of offers to their first-year students.