mjhjmtu

I feel very thankful for marmot for helping me with this problem, but I have another problem. It seems like tkz is actually very hard to understand. I have added the usetkzobjall command and it does actually work, although as I get further in the paper (tkz-euclide) it doesn't work anymore! Here is an example:

documentclassarticle
usepackagetikz
usepackagetkz-euclide
usetkzobjall

begindocument

begintikzpicture[scale=1.5]
tkzInit[xmax=5,ymax=5]tkzGrid[sub]
tkzDefPoint(1,2)A tkzDefPoint(3,4)B
tkzDefPoint(3,2)C tkzDefPoint(3,1)D
tkzDrawSegments(A,B A,C A,D)
tkzDrawPoints[color=red](A,B,C,D) tkzLabelPoints(A,B,C,D)
tkzFindSlope(A,B)SAB tkzFindSlope(A,C)SACtkzFindSlope(A,D)SAD
tkzText[fill=Gold!50,draw=brown](2.5,0)La pente de (AB) est : SAB
tkzText[fill=Gold!50,draw=brown](2.5,-.5)La pente de (AC) est : SAC
tkzText[fill=Gold!50,draw=brown](2.5,-1)La pente de (AD) est : SAD
endtikzpicture

enddocument 

Here is the result:

See the xcolor package documentation for explanation.
Type H <return> for immediate help.
 ... 

l.17 ...brown](2.5,0)La pente de (AB) est : SAB

? 

Process has been terminated ...

This is what it's supposed to look like:

You haven't shown the whole error message. It says

! Package xcolor Error: Undefined color `Gold'.

See the xcolor package documentation for explanation.
Type H <return> for immediate help.
 ... 

l.16 ...own](2.5,-.5)La pente de (AC) est : SAC

Try typing <return> to proceed.
If that doesn't work, type X <return> to quit

The key part being the first line.

xcolor does have a lot of predefined colors, but they are not loaded by default. For Gold, you need to load xcolor with the svgnames option. Of course, you're not loading xcolor explicitly, that's done by TikZ, but you could do

documentclass[svgnames]article

which will pass svgnames to xcolor when it's loaded. With that modification your code runs without error.