So for the most part, in all cases of borrowing money to pay for something will report to a credit report (experian, transunion or equifax). So when you finance through dell, you really would finance through Dell Financial Services (DFS) which is a separate company owned by dell. They would report this to your credit report as a loan or revolver (not sure exactly how dell does it). The more things reported to your credit report, the more your credit report is considered thicker. A credit score is a good indicator but isnt the only factor in making a lending decision. For example someone with a credit score of 700 and has 1 car loan and 2 credit cards for 5 years, would probably have a better chance at approval versus someone who has a 780 credit score and only 1 credit card for 1 year. because there is more history to them.
I dont think i even answered what you are looking for, but if you look for a website called myfico (they make the FICO scoring model), theres a lot of info on credit and financing and all the things that can be learned about. As someone who holds a BSB finance and works for a bank in the underwriting department. credit is complicated good thing, but always know what your getting yourself into and never go beyond your means. I always recommend that someone who is 18 and has consistant income should get a small credit card or loan like through dell to start building their credit. Credit i believe is something that needs to be taught more in schools, so that consumers can save money and understand how to get some good rates. also theres still some predatory shit out there (like best buy financing) that i believe shouldn't be out there and can catch people by surprise.
as a side note as i reread your question. Interest rate only affects how much you pay, having a higher or lower interest rate will not affect the credit score itself.