This is fairly obvious: you wear your karate suit. A karate suit is basically a pair of loose white cotton pyjama things which you can buy from any martial arts shop. I believe I got mine via Amazon. The only thing to decide is how much you want to pay, and what size to buy. Do make sure you buy a karate suit, not a judo suit, which is heavier and thicker. If you are a novice and still not entirely sure whether you are going to carry on with this mad karate enterprise, then you will want to buy yourself a nice cheap kit. It will come with a white belt, which is the first colour of belt you will need.
As anyone knows who has ever worn white trousers, white or 'nude' underpants are essential, unless you are something of an exhibitionist. Personally, I think thongs are unwise, though you are less likely to lose your trousers during karate than judo. Women and girls can wear a T-shirt. In judo this has to be white, but as far as I can see, this isn't strictly policed at my karate club. And that, my friends, is it. Oh, apart from a good stout sports bra if you are blessed bosom-wise. No jewellery, no shoes, no socks. Undies, white pyjamas, T-shirt (women) and a belt. (If you are sparring, you'll need shin/foot pads and mitts; and a gum-shield if you are under 18.)
Today I went to my second karate grading. I wore my red belt. By happy coincidence red is the correct liturgical colour for Palm Sunday. This was some slight consolation for spending my morning at King Eddie's leisure centre rather than in Lichfield cathedral. Despite cocking up some of my renraku waza (combination techniques), I managed to pass, so from now on will be allowed to wear a yellow belt. It will be awarded at my next training session. Again, by happy chance, this is the correct liturgical colour for Easter.
Probably if you are going for a higher grade you will have some kind of totemic garment which you will don with trembling fingers as part of your preparation for the ordeal that lies ahead. Your 'lucky' trousers, your old 1000 wash grey T-shirt. But I am still dabbling in the shallows of karate and quite blithe about the whole thing. To be honest, after the adrenaline-drenched horror of judo dan gradings, when I faced psychotic teenage girls across the mat and got repeatedly slaughtered, karate gradings--tra la la--hold few terrors for me. Sssh! Don't tell sensei I said that.