Read Texmaker's documentation and then follow the instructions step by step. Here are the three main steps:
1. Configuring Texmaker
1.1 Configuring the editor
1.2 Configuring the latex related commands
1.3 Configuring the spell checker
2. Editing a TeX document
2.1 Usual commands
2.2 Setting the preamble of a TeX document
2.3 Structure of a document
2.4 Browsing your document
2.5 Formatting your text
2.6 Spacings
2.7 Inserting a list
2.8 Inserting a table
2.9 Inserting a "tabbing" environment
2.10 Inserting a picture
2.11 Cross References and notes
2.12 Inserting math formulae
2.13 Using the "•" place holders
3. Compiling a document
3.1 Compiling
3.2 The log files
3.3 Synchronization source-pdf with Synctex
3.4 Using XeLaTeX
Read Texmaker's documentation and then follow the instructions step by step. Here are the three main steps:
http://www.xm1math.net/texmaker/doc.html