In Matthew 3:6 we have the first use of the word βαπτιζω (1/77), meaning to baptize, to soak or dip in water, or to pour over the head and ears.  From the 7th edition of An Intermediate Greek-English Lexicon by founded upon Liddell and Scott's Greek-English Lexicon

Who is baptizing?  John the Baptizer
What is he baptizing?  Well from v5 we see that he is baptizing many folks who are from the region were coming out to him to be baptized.  
When? Still the first century
Where is he Baptizing?  Well this time it narrows down a bit. John is baptizing folks still out in the wilderness, but in particular at the River Jordan.  This river has some significance throughout Israel's history, in particular this is the river that parted when Israel entered the promised land. 
Why is he baptizing them?  They come to him to be baptized after confessing their sins.  Now this is a bit surprising because people typically confessed their sins in the temple, brought sin offerings to the temple, etc.  This connection with sin, means it comes not from man, but from God. 

How is he baptizing them? By washing them in the river Jordan

In Matthew 3:7, we have the first use of the word, βαπτισμα (1/20) meaning baptism. 
Who is baptizing? John the Baptizer
What is he baptizing? Surprisingly, not just lay people but even the Pharisees and Sadducees have come to be baptized. But this section leaves us a bit unsure as to whether or not they are baptized. We do know that there were Pharisees who did repent, and were followers of Christ.  
When could they be baptized? When they repented, the trouble with the Pharisees and Sadduccees was that they were lacking repentance. They believed they would be ok because they were children of Abraham by the flesh. Repentance is not about who your parents are, or even about how many good works you do.  Repentance is the confession that I am a sinner, and I deserve punishment for my sin, but rely solely upon God's grace. 
Where does this happen? At the Jordan
Why are the people being Baptized? It is more than just confession of sins, they were also fleeing God's wrath. So the people who are getting baptized are fleeing the wrath of God which will toss every tree not bearing fruit into the fire.

Let's return to our key question. Is John's baptism from heaven or from man. If Baptism is man's work, then how would man's works hide us from the wrath of God?