If your relationship matches to one and only one record, you can simply refer to the field from the related table in your calculation such as:
Do some calculations here + StudentTuitionHistory::TuitionAmount
In a field of type calculation, this will produce an unstored calculation field so you may need to consider the consequences of that.
A number field with an auto-enter calculation could also use this expression, but it would not automatically update should the value from the related table be later modified so you get a stored, indexed value, but with limitations.
Some developers find that scripts performed from script triggers work better if they need a value that is always up to date and that is a stored, indexed value. This takes much more effort on the part of the developer so I don't advise tis option unless you have a specific reason that precludes other options.
If your relationship does not match to the correct single record, you'll need to either set up a different relationship that does or use one of several other means that exist for calculating the needed value.