You need:
Refractometer for testing newly made saltwater for SG.
Test kits for ammonia, nitrite and nitrate. Getting started a api saltwater master kit will do and will have all of those in it. Can get them at petsmart or petco. They are fine to use to get started. You can get better kits later.
RO/DI unit is preferred for making clean water. Not needed at first and you should be able to get RO/DI water from your LFS for now.
https://www.bulkreefsupply.com/ Is a good choice for one.
Try not to use tap water to make saltwater with. Depending on what’s in your water, it’s not the best choice to use because of the chlorine/chloramines in it and heavy metals.
Your LFS maybe a good source for information, but sadly some are not! Bad ones will sell anything to you and say “it’s fine”. So be careful and when in doubt, ask us here!
Anytime you need questions answered, ask the question and the type in #reefsquad and a ton of knowledgeable reefers will respond with solid answers!