There are many ways to compare two paintings, but to make it easy some ideas:
First look at the two paintings on their own, what do you see? (not what do you think it means, but really just what you see.)
What is the technique, the composition of the painting?
What do you know about the time the painting was made, what were the general ideas of the style it was painted in, and can you also see the elements of that style in the painting (and if so, what are they)? Use wikipedia, google, art-history books etc.
Could you, if you look at the technique, art history, and the composition, make an educated guess what the artist would have meant with his or her painting?
Now that you have your analysis for both paintings, you look for the differences and the similarities. Are there any elements that are the same, what are the big differences, and why would that be, look at the different times the painters lived in and their ideas about art and the world, and how they translate their view into their art.
You can also add a personal conclusion, what painting grabs you more now that you have analyzed them both, and why?