If you have never been to World War 2 concentration camp you really need to prepare yourself for this experience. A little reflection beforehand on the history and context may assist. You also must know that you are going to see, smell and walk through something truly horrific. Majdanek has been very well kept and if you have been to the busier more famous Auschwitz you may feel the lack of tourists and chatter lends itself to an even more chilling experience. I have been a number of times with my husband. We did not engage a guide because sadly my in laws know all to well the history and havoc of this place. The smell is something I will never forget, especially the bins of shoes.
If you do engage a guide, and I suggest you do if you don’t have an intimate understanding of the history. You need to reserve a guide and they do offer a few languages outside of Polish. This is a service you must pay for, otherwise entrance to the museum is free. The website has all the information you need, plus additional resources. http://www.majdanek.eu/index.php
Finally, remember where you are going and dress and behave appropriately. It is recommended that you do not take children under 13 years of age and lighting candles is prohibited.
The museum is stunning and the work to maintain the history of those who have perished is commendable.