The average mass is the sum of the measurements divided by the number of measurements.
I assume "deviation mass" means "standard deviation of mass measurements". Khan academy has a good discussion of how to calculate standard deviation at:
https://www.khanacademy.org/math/statistics-probability/summarizing-quantitative-data/variance-standard-deviation-population/a/calculating-standard-deviation-step-by-step
The absolute uncertainty is a measure of the maximum and minimum deviations from the mean/average. In this case it looks like the maximum weight is 5.3kg and the minimum weight is 4.8 kg, so the absolute uncertainty would be (mean) +/- (5.3 - mean)
The relative uncertainty is (absolute uncertainty / mean) * 100%.
"Determination of uncertainty" is somewhat ambiguous - maybe your instructor is asking you for a discussion of how uncertainty is calculated/determined, a summary of your uncertainty calculations, or for a final calculated uncertainty value. You might look at your course notes or ask your instructor for clarification.
