There are 5 major impurities (things that are not clean or pure) that we Muslims should be aware of. These are :-

1. Urine
2. Excreta
3. Blood
4. Matter or Pus
5. Alcohol 

Of course, there are other impurities. But we have mentioned the ones that affect you. 

Besides keeping our bodies clean it is very important for us to keep our clothes clean. If any of these impurities stains our clothes, then our clothes will become unclean. If this happens, then one has to wash one's clothes under running water at least 3 times for it to become clean. We also have to make sure that the clothes be squeezed thoroughly after each wash to remove all stains of the impurity.