HOW DO I use EPSOM SALT/Dolomite lime

I asked in my post but RIU seems to not be wanting to help me today
Please real fast i know it must be easy just never worked with it and dont wanna fuck my babies over.
How do i use epsom salt correctly?
Same with the lime stuff?
And can i buy either of these at my local Target or grocery store? or shall i have to go to my grow shop?

dolomite can be had from your local nursery usually
best mixed in with your soil, so it's a premix kind of thing
1 tbsp per gallon of soil really helps on ph and does add calcium and magnesium to the soil

well thank you for the advice, though this wont help me as of now due to i have to give this to my about to be 4 week old plants.
Epsom salt would be my first choice due to it has mag def and lock out of k i belive though, the salt will help if i can figure out where to get it and how to use it lol.
Like do i just put 1 teaspoon of it in a gallon of nutewater or clear PHed water and do i let it sit to disolve or something and then water or do i flush the plants. this is all something i need to know:/

thought that might be the case, dolomite is slow but some do use it as a top dressing
i had the same problem where i thought i had a magesium def., tried the epsom salts
didn't help in my case, i think real magnesium def. are fairly rare, the lock out sounds more likely
i don't recall the exact amount, but epsom salts go a long ways, it's less than 1 tsp per gallon
memory was it was closer to 1/4 tsp per gallon