Are you avoiding using rect() on purpose?  http://processing.org/reference/rect_.html

You can set the color of lines and points by using 3 arguments to the stroke() method.  stroke(255, 0, 0) will draw everything in red for example.

There's no way to make point() bold - it's always one pixel in size.  The best alternative is probably to replace your call to point with: ellipse(x, y, 10, 10).  Add ellipseMode(CENTER) to setup so that the ellipses end up in the right place.

You can bold the point by using strokeWeight(int number) function, just type something like strokeWeight(5); and it will thicken all the lines and points that are drawn after that function.
For the rectangle, try using THIS. If you use shapes, you can easily fill it with the fill(); function. But I still don't understand why exactly are you drawing that rectangle the way you are because when I run your code, there's a little black line which looks weird.

here's a version of your code written using the beginShape() function

1. smooth();
2. size(400,400);
3. background(255);
4. int x = 100;
5. int y = 200;
6. fill(255, 0, 0);
7. stroke(255, 0, 0);
8. beginShape();
9. vertex(x-5, y-30);
10. vertex(x+5, y-30);
11. vertex(x+5, y);
12. vertex(x-5, y);
13. endShape();
14. stroke(0);
15. strokeWeight(5);
16. point(x-5, y-30);
17. point(x+5, y-30);
18. point(x+5, y);
19. point(x-5, y);

of course you can use rect, just use x-rectWidth/2, y - rectHeight

press any key to see the change from mataarsak lines to my rect

1. // rect
2. int x = 100;
3. int y = 200;
4. int rectWidth = 10;
5. int rectHeight = 30;
6. void setup() {
7.   smooth();
8.   size(400, 400);
9. }
10. void draw () {
11.   background(255);
12.   // draw a rectangle like this :
13.   line(x, y, x-5, y);
14.   point(x, y);
15.   stroke(166);
16.   line(x, y, x+5, y);
17.   line(x+5, y, x+5, y-30);
18.   line( x-5, y, x-5, y-30);
19.   line(x-5, y-30, x+5, y-30);
20.   stroke(222, 2, 2);
21.   if (keyPressed) {
22.     fill(245, 0, 0);
23.     rect (x-rectWidth/2, y - rectHeight, rectWidth, rectHeight);
24.   }
25. }

@matarsak: ?