welcome to the forum! you're gonna want to start with a few key supplies, being a tank, salt, a refractometer or hydrometer, a saltwater test kit, a heater, some dry rock and some sand and some beneficial bacteria .
a lot of people will recommend to start with the biggest tank you can get, although it is sometimes easier to have a stable environment it's usually just as easy to have a small tank as long as you keep up with it. i'm currently keeping a pair of clownfish in a 10 gallon tank. so for the tank, i would either go the route of an all in one tank (like a biocube. benifits of something like this is it comes with a light so you don't need to buy one) or a very basic tank and a hang on back filter (like a basic 10 gallon tank with an aquaclear 70 hang on back filter) if you're only wanting clowns to start i'd probably say get a 10 gallon tank, you'll spend a lot less on supplies.
you'll want to start with good quality fresh water. if you have the funds to get a RODI unit to filter your tap water, but if you don't then you'll want to get a water conditioner/dechlorinator. once you're there you can mix your salt into it. i recommend using a refractometer over a hydrometer because it's easier to see your salinity, you can get them for pretty cheap on
amazon. i like mixing to about 1.025 salinity, but anywhere from 1.023-26 will be fine for a fish only system.
now that you have your first batch of saltwater mixed you can fill your tank. of course you'll want to put your sand and dry rock in whatever way you want. you can put in your beneficial bacteria and let the cycle start. wait a few weeks before adding fish and you'll want to test the water regularly. you don't really need to worry that much about alkalinity until you get corals. you'll also want to do weekly water changes of at least 15-20%. also especially in small tanks you want to watch out for water evaporation and refill whatever evaporated water with fresh water.
once you get your fish i would start by feeding lightly. a small amount once per day is fine. clowns are pretty easy to keep and i can say i've had a few clowns that i've really neglected in the past when i was very new to reefing and they lived. just try to learn as much as you can.there's a ton of good youtube channels and videos you can learn from. good luck