I hope that this post will be able to answer all these questions, as many people might wonder them.
What is the Priesthood?: The priesthood is the power of God, and the authority to act in his name. It has been given to prophets since the beginning of time so they can run Gods church upon the earth. Multiple times this authority has been taken away due to wickedness and unbelief, but because God loves us he always restores it again. When Christ came he gave this authority to his chosen apostles so they too could bless the lives of their brothers and sisters. After Christ was crucified there came a falling away (2 Thessalonian 2:1-3, Amos 8:11-12) The priesthood authority was once again taken from the earth for a period of time.
In the early 1800's Joseph Smith, having been visited by God the father and his son Jesus Christ, and called to be a prophet, was given once again the priesthood authority. John the Baptist, restored the Aaronic Priesthood, and later Peter, James and John as resurrected beings restored the Melchizedek Priesthood.
The priesthood authority was then passed down from Joseph Smith to other worthy members of the Lords church. Now days, all worthy males, ages 12 and older can hold the priesthood.
Why the Priesthood is needed?: Because this church is the Lords church and not mans, all things done within it must be done God's way by those he has chosen. "Ye have not chosen me, but I have chosen you and ordained you..." (John 15:16). There are things the lord has commanded all of us to do, like being baptized, and when they are done without the priesthood authority they are invalid, because God did not authorize them. God is a God of order, and if everyone were allowed to baptize and do it their own way, we would lose the beauty and the meaning of these sacred ordinances. Kind of like if every single person was a cop, then there would be no reason for one anymore.
How can the Priesthood affect my life?: Though only worthy males are able to hold the Priesthood, this power blesses the lives of all people. "the powers of heaven cannot be controlled nor handled only upon principles of righteousness." " (D&C 121:36). The priesthood is a blessing is so many different ways, one of those is the ability the bless those who are sick or afflicted in any manner. this goes along with the verse in James 5 verse 14-15 "is any sick among you? let him call for the Elders of the church, and let them pray over him, anointing him with oil in the name of the Lord: And the prayer of faith shall save the sick..." By the same power that Jesus had to heal the sick, worthy males who hold the priesthood can heal the sick. The other important way the priesthood can bless any families life, is that it is by this power that families are sealed together for time and all eternity. Only through the priesthood of god, can families be eternally united. This is something that every family should desire, and one all of us should seek after.
I know that the priesthood is real, I know that is so essential to the church of god. With it we have everything and without it we have nothing.