please help

That's a good, and useful question.  Understanding the relationship between scales and chords is an important thing.  I've got a couple of sticky's up on scales that would be worth reading.

The short answer is that each note in a scale will relate to a different kind of chord, because of the chords that will be built from the notes of that scale.

So an example.  Lets use G major.

The G major scale is

G A B C D E F# G

Triads make up chords, so G major chord is

G B D

That's pretty standard stuff.

But lets move up to the II in G major, and build a triad.

That gives us

A C E  : A minor.

If we move to the III,

B D F#: B minor.

The IV

C E G:  C major

The V:

D F# A:  D major

The VI:

E G B:  E minor

The VII:

F# A C:  F# diminshed

So if you're able to play the major scale, you can determine which triads are going to be appropriate for the key.

From a scale perspective,  the various modes are what you need to know.   You've probably heard of "relative minor" scales.  What that means is that each major scale has a minor scale made up of the exact same notes.  For G major, it's E minor.

G major scale:

G A B C D E F# G

E minor scale:

E F# G A B C D E

The relative minor for any major scale is indicated by the VI of the scale, so it's easy to locate.   

Each of the modal scales is determined in the exact same way.

A Dorian is derived from G major.  Exact same notes.  You will also note that you can build the aforementioned triads from this scale.

A B C D E F# G A

B Phrygian:

B C D E F# G A B

C Lydian:

C D E F# G A B C

D Myxolidian:

D E F# G A B C

E Aoelian (a.k.a E minor):

E F# G A B C D E

F# Lydian (a.k.a freaky jazz guy )

F# A B C D E F#

So all of that is derived directly from the major scale.  If you know the scale patterns, all of this will fall out of it, and you don't have to memorize hardly anything.

Here's a practical side of it that you can apply to the fretboard right now.

I'm sure you know the minor pentatonic scale pattern.  It's one of the 1st things you learn.  Lots of wankery is to be had with it. 

Here is A minor pentatonic.  This pattern is completely portable, so you can move it anywhere.

---------------------------5-----
----------------------5-8--------
-----------------5-7-------------
------------5-7------------------
-------5-7-----------------------
--5-8----------------------------

Using that as an example:

If someone is playing in a major key, you can always play a lead using that major scale.  You can also slide your finger down the neck three frets, and play the minor pentatonic scale pattern from there, and you will be fine.

So for this example, if someone is playing a song in C major, find C on the sixth string (8th fret).  You can play C major from there.  You can also slide down to the 5th fret (A), and play the pentatonic minor pattern from there, and you're still in key.

Just for comparisons sake, here is C major pentatonic.  Can you see how the patterns line up?

---------------------------5-8---
----------------------5-8--------
-----------------5-7-------------
------------5-7------------------
-------5-7-----------------------
----8----------------------------

sometimes you can use modes if the song is in G major I use the E minor scale the same holds true for all keys the 6th interval of any key is its relative minor so in the G scale the notes
G A B C D [E] F# G could be numbered as 1 2 3  5 6 7 8 and thats how you find the relative.
1 3 3 4 5  (6)  7   8 
                 ^
                 ^ is the relative minor in G (E) you can also do that with C  C D E F G (A) B C
                                                                                                       1  2 3 4 5 (6) 7  8
                                                                                                                      ^
                                                                                                                      ^ 
                                                                                                                relative minor
keep in mind that there are sharps and flats and you must know which notes are sharp or flat and the only way to do that is with basic theory Jerome can help you with that better then I so good luck with it