Very Simple Noobie Suspension Questions

OK I am a noob.
I dont know the most basic things so here we go..

I have a 1990 yz125. (It has the white frame and pink upside down forks)

1. How do I make the suspension and the bike feel a bot more ridgit and stiffer. (I just rode a mates 01 cr125 and I really like the way his suspension was.0

2. All I know that looking at the top of the forks there are 2 brass screws. The ones off to the side are the ones to realease nitrogen gas after you tie the bike down.

What do the 2 in the middle do?

My bike has very soft suspension ATM. I weigh 72 kilos and it feels very soft and plush. I dont like that. I want a solid feeling bike like my mates 01 ktm 200exc.

What do the little screws on the bottom do?

Now rear shock:
I used to have a modified car with very nice cusco coil over suspension. Anyway the height could be adjsuted by screwiung or unscrewing the rings around the schock that compress the spring. Is the same way to make a dirt bike higher and lower? How do I use this thing?

Also how can i make it more stiff?

THanx Sorry for being so unknowlegeble in this area.

regards,
Dmitri.