At the end of last week's Parshah, Shemini, we began to discuss the laws of purity. These laws, called the laws of Tumah and Taharah, are continued in this week's portion.
The first topic discussed is a woman who has given birth. She is impure for a set amount of days, then she immerses in a mikvah (as mentioned last week, this is a special body of water that makes a tameh [impure] person tahor [pure]) and brings a sacrifice.
All baby boys are to be circumcised at eight days old; we call this the brit milah.
Next topic of discussion is a unique disease called tzaraat. It is different from other illnesses because it has a spiritual cause and makes a person impure. If a person thinks he may have this affliction, he must go to a kohen and the kohen looks for signs to see whether it's the impurity of tzaraat or just a regular illness. The Torah teaches the kohen which signs to look for to identify the disease as tzaraat.
Why in several parshas is the name of Hashem given in three different forms: Ado, Elokim, and Yud Hey Vav Hey? In some mishpot His name is referenced twice or even three ways i.e. I am Hashem, your Ado, the one and only Elokim (or something like that). Is there some significance in using one name over another or all three?
Each name has a different significance and speaks to a different aspect of Hashem. Yud Hay Vav etc. is referring to His attribute of Mercy and Elokim his attribute of might or severity. Ad-nay has to do with His Sovergneity - from the word Adon. Sometimes Rashi will explain why a certain name is used, or commentators will explain the message behind having a combination of names in one verse. To get a general overview of this please see How Many Names Does G‑d have?