Right, you'll want to acquire a good liquid-reagent based test kit. I'm assuming you're here to learn about fresh water tropical fish, right? If so, then many of us use the API Freshwater Master Test Kit (about $30 US, 20 pounds UK?) or the Nutrafin Mini-Master Test Kit. These will have the essential tests for ammonia, nitrite(NO2), pH and nitrate(NO3) and they'll have enough accuracy to do what needs doing.
Water changing is a skill and you'll need to learn the techniques and the ways to know how much water to change and how often to change it. It'll take you answering some questions to the members here, so we'll need to know a bit more about your situation and goals.
Cleaning out your fluval will not need to be done for a long time as it will need to be undisturbed during your initial fishless cycle (or Fish-In cycle if you've been given bad advice and have fish in too soon.) Eventually, you will want to establish a habit, perhaps, of cleaning it every month, at which time you'll clean the media in TANK water, not tap water! Regular monthly cleaning is a very good habit.
Regular weekly glass, ornament and gravel cleaning is an even more important habit as its also combined with the all-important water change which will remove the build-up of trace metals and organics that we can't afford to test for or don't have time to test for.
Good luck and tell us about the size of your tank and when you started and what your plans are!
Welcome to TFF, ~~waterdrop~~