"i heard that there's 4 switches,
brown, red,blue and green
can anyone explain to me briefly what distinguishes them all apart?"
There are Cherry MX Switches, a brand of mechanical switch that is considered the standard.
There 3 types: Linear Tactile and Clicky. They also make a locking switch. https://deskthority.net/wiki/Cherry_MX Most recently they have introduced gaming marketing "Speed Switches" Which offer a low actuation force, as well as shorter travel distance.
In the 3 categories switches are then sub-divided by actuation force. All of these switches cane be identified by the color. They have recently also introduced the clear variants of all of their switches for LED back lighting purposes.
Now there are also many other mechanical key switch manufacturers including Gateron (https://mechanicalkeyboards.com/shop/index.php?l=product_list&c=77) which are a Cherry MX clone, Razer has also recently developed their own switches (https://www.razerzone.com/razer-mechanical-switches). There is also a company Matias making Alps clones, which were a popular switch in the 90's IBM keyboards.
https://mechanicalkeyboards.com/mechanical_switches.php?brand=
Above is a link to a site that shows more brands and types, and describes their function/use.
Really they only thing to do is to try out some key switches/keyboards and see what you like. I personally, despite not gaming much, use CherryMX reds. Low actuation force, linear, smooth, and pretty quiet. Many people appreciate the tactile switches for typing, and hardcore typist seem to lean towards the clicky switches (like the blue).
Personally I think accuracy has a lot to do with it. If you are prone to mashing keys, the reds will be misserable, where the blues could really improve speed and accuracy. However if you're accurate, a linear switch can reduce fatigue, and not drive people around you crazy.
Despite the links I shared, there are countless other, more obscure mechanical key switches, including hall effect switches.
One thing to consider also is key caps. You are going to find it much easier to find key cap sets that fit Cherry MX switched, and their clones than any other design.
It really is up to your preference in regards to switched. Then once you choose a switch, shop for a keyboard that offers the features you need (n-key roll over/anti ghosting/macros/pass throughs/10 keyless or full size/backlighting (RGB)/etc). You can get a good mechanical keyboard these days for a reasonable price if you stick to the basics. I use a sub $100 CM Storm QuickFire Pro (https://www.amazon.com/CM-Storm-QuickFire-Pro-Mechanical/dp/B007VDOOBU). There are even cheaper options on the market these days with all the Cherry Clones offering competition in the market.
It really is all about preference, I would just get the cheapest board with the switches you like. Everything else is nit picky BS. People can and will justify $500 keyboards because they are stupid. I recommend the sub $100 price point for best results and avoiding feeling like an idiot for wasting money on frivolities.