Decide on three or four aspects that you could compare and contrast. For example, the use of Christian elements and Pagan elements, the speaker, and the reason for a nomadic lifestyle. Both poems are also broken into essentially two parts--the first, explaining who the speaker is and what is going on in his life and the second addresses man's fate and/or relationship with God.
In The Seafarer, the speaker is a Christian who absolutely loves the sea. He can not think of anything else, even though it is not an easy or comfortable life. He prefers it to the life of ease and physical comforts that living on land provides. The sea is ingrained in him, and he longs to be on the water when he is not. You would probably understand this longing if you compared it to something you enjoy doing that would effect you negatively should you not be allowed to enjoy it any more--sports, music, shopping, or surfing the internet might be among the pasttimes you enjoy most.
In the second part of the poem, the speaker gives advice about how to live life. It is very much like a prayer to the Lord as he finishes with "Amen".
In The Wanderer, the speaker has lost his home, family, friends, and the generosity of his king. He roams the land looking for some friendly face to take him in where he may find comfort in human companionship. He addresses man's fate in the world in the second part.