A great source of data and an explanation to go with it is an Internet site called the Data and
Story Library (DASL) maintained by Carnegie Mellon University. Go to that site and examine the example on the relationship between brain size and intelligence. Use multiple regression to predict full-scale IQ from brain size (MRI-count) and Gender. The address is https://lib.stat.cmu.edu/DASL/Datafiles/Brainsize.html.
(You will have to convert Gender from Male and Female to 1 and 2. Your software probably has a recode or compute command that will do so.)