What does these commands do all together

Question

The university gave us a standard tex file for our thesis, and they made it based on Scientific Workplace.

When I opened it with MikTex, many problems occured. I fixed most of them and I'm left with this one :

\fancyhf{} \cfoot{\thepage} \lhead{Conclusion} \setlength{\headheight}{0.5cm}
\renewcommand{\headrulewidth}{0.7pt}\

i don't understand its role.

A second thing is that I used \usepackage{xcolor} but unable to use the command \color{Blue} as it says that it's undefined

Thrid thing is that my Table of contents has some red squares surrounding titles, how can I remove them ?

These are the packages I used

\documentclass[a4paper]{book}%
\usepackage{amssymb}
\usepackage{eurosym}
\usepackage{amsfonts}
\usepackage{amsmath}
\usepackage[utf8x]{inputenc}
\usepackage{color}
\usepackage[doublespacing]{setspace}
\usepackage{geometry}
\usepackage{graphicx}
\usepackage{hyperref}
\usepackage{fancyhdr}
\usepackage{float}
\usepackage{xcolor}
\usepackage{rotating}