Power : Life protection, Avoid from danger, Wealth, Prevent Dark Magic and Evil Spirits,  Attraction money and lucky, Danger Obstacle cease, Give metta merciful, Triumphantly, Harm proof, Weapon proof, Loving Kindness, Change Bad Luck to Good Luck, Bring Lucky and Happiness, Wishes be Fulfilled, Bring Prosper to Business, Invulnerable, Successful, Good Trade, Halo, Powerful.

What do we have to do before we wear the amulets?

Before wearing amulets, please do this way :
- Make your mind calm, think of all your goodness you have done, and  focus all your faith to the Buddha 
- Put your amulets onto your hands, join your hands together 
- Breathe in deeply and slowly
-Then chant 3 times of this initial Mantra:
NAMO TASSA  PHAKHAWATO  ARAHATO  SAMMA  SAMBUDH  TASSA 
    The chanting verse means we are now praying respect to the Lord Buddha who has done the great goodness. Then request with your own language for his help, say "I, a humble one, invite the Lord Buddha and Luang Phor..... [name(s)] to sit on my head to protect me all day long and bring me a good luck, a victory, and a fulfilment of all my wishes."

    The meaning of this Mantra is-may Lord Buddha, Dhamma and Sangkha or Triple Gems bless all my request 
successful. And then wear the chain of amulets onto your neck. 
Just take it out off your neck and put all amulets in your hands. Join your hands together, say thanks to the Lord and Luang Phor(s) that protect us and let us come back home safely. Then bring them onto a high place. 
Yes, there are some restrictions: 
-Don't bring amulets with you when you go to the low and improper place such as a brothel. 
-Don't wear amulets when doing sexual activities.
-Don't go underneath the improper things such as the lady's skirt or someone's shoes, except you are on the inevitably compulsory environment such as going under a bridge or working in a skyscraper, etc.
Yes it is. But it also depends on the quality of your mind. The late  Luang Phor Ngern of Wat Don Yai Hom, Nakorn Pathom Province, one of the greatest guru monks, once said that: the number-one mind with full-hearted trust in Lord Buddha's miracles, the gun will not bang or misfire; the number-two mind, the gun bang but the bullet misses; the number-three mind, the gun bang and the bullet hit the target but never penetrate into the body. So, when you hang Buddha amulets on your neck, you must have faith and trust on the Buddha!!   
1. Who creates it? If the amulet is created by the great guru monk who has Samatha and Wipassana Yana ( the great knowledge on advanced meditation), he could invite Lord Buddha of every epoch and all Arahants to charged the great power onto the amulet.

Then say " BudDhang PraSitThiMae DhamMang PraSitThiMae Sangkhang PraSitThiMae." 

What do we have to do if we want to take the chain of amulets out off our neck?

Any restriction when wearing Thai Buddhistic amulets?

Is it true that the Buddha amulet can protect firearms? 

The Buddha power in an amulet depend on: 

2. How clean and how good-intended on that creation. In the old times, almost all guru monks had very clean and good-intended mind because they aimed at the future-to-be Buddha, so they devoted their lives to help build a lot of facilities in many temples. That means tons of money are needed to buy raw materials for construction, so amulets were created to present to donors as a gift in exchange. The good examples on this are Luang Phor Doem of Wat Nong Pho and Luang Phor Parn of Wat BangNomKho, both Luang Phors helped build more than 30 temples!! At present times, we still have very good guru monks but not as many as in the past. So, if you would like to collect the newly-made amulets, you should have to ask yourself with some of these questions: who create them and do they have advanced meditation knowledge, what for, and who are invited to perform the blessing ritual, etc.  

Information from many amulets books