Thanks for the questions.
- How did priests get their ability to bless things and people?
First, it's important to mention that though priests perform special blessings in the name of the Church for specific reasons, ordinary baptized people, like you and me, can also bless other people. For example: Parents are encouraged to bless their children.
Priests receive their special ability to bless or make holy certain material [and/or] people through their ministerial priesthood. A priest becomes a priest through Holy Orders, one of seven sacraments Jesus instituted before ascending into Heaven on Ascension Thursday. Only through His Priesthood can sacramental grace enter the world for our spiritual benefit. For this reason, the Catholic faithful should always periodical thank their pastors and priests for their priesthood.
- Where in the Bible does it show this?
Your question assumes that a priest blessing something or person has to be in the Bible for it to be true.
This is not true. In the Catholic Church we believe in both Oral Tradition as well as the Written Scriptures.
It is both the oral and written teachings that have been passed down to us by Jesus and His Apostles through the Pope and Catholic bishops.
If you were looking for the Bible basis for blessings in general these passages should help:
- What exactly is a blessing?
The Catechism tells us:
|1078 Blessing is a divine and life-giving action, the source of which is the Father; his blessing is both word and gift. When applied to man, the word "blessing" means adoration and surrender to his Creator in thanksgiving.
I hope this helps,