There are road bike forks and mountain bike forks, for road bikes you can have steel, alloy or carbon forks and they can be straight or with a rake, which is a bend in the fork, the straight and the raked forks do the same thing, but the rake can give more of a comfortable ride.
For mountain bikes you have to get suspension forks, the original suspension forks had a spring in each arm.
You could use different spring for different weight riders and surface conditions, but they were very basic. Forks evolved to have oil or air damping, which is adjustable and you could have different rebound. All very complicated but you could ride over any conditions and in all weathers.
There are many suspension forks on the market, probably the best known is Rock Shox, but there is also Manitou, Marzocchi, RST and Girvin.
You have to buy forks with a steering column depending on which kind and size of headset you have.
There are different size columns, 1 inch, 1 1/8inch and there is occasionally 1 1/4 inch, and it has to be threaded or smooth for standard or aheadset.
Forks are very important, as you really need them to steer your bike in the direction you want.
I have an Easton SC70 road fork on my Trek 2000. It has a 43 mm rake. I love the feel and responsiveness of it, but I find it very unstable. Twice in the last year the front wheel has slipped out from me when I didn’t expect it, causing me to lose control and land on my right hip both times. Do any carbon fork manufactureres make one with a 50 mm rake? I would like something more stable so I can save my body.Thanks.