The following table shows some basic HTML tags, with short descriptions.
There are many online HTML guides; the table below is based on the HTML cheat-sheet on webmonkey.com

Basic Tags

<html></html>
Creates an HTML document

<head></head>
Sets off the title and other information that isn't displayed on the Web page itself

<body></body>
Sets off the visible portion of the document

Header Tags

<title></title>
Puts the name of the document in the title bar

Body Attributes

<body bgcolor=?>
Sets the background color, using name or hex value

<body text=?>
Sets the text color, using name or hex value

<body link=?>
Sets the color of links (i.e. URL’s), using name or hex value

<body vlink=?>
Sets the color of followed links, using name or hex value

<body alink=?>
Sets the color of links on click

Text Tags

<pre></pre>
Creates preformatted text

<hl></hl>
Creates the largest headline

<h6></h6>
Creates the smallest headline

<b></b>
Creates bold text

<i></i>
Creates italic text

<font size=?></font>
Sets size of font, from 1 to 7)

<font color=?></font>
Sets font color, using name or hex value

Links

<a href="URL"></a>
Creates a hyperlink

<a href="mailto:EMAIL"></a>
Creates a mailto link

<a name="NAME"></a>
Creates a target location within a document

<a href="#NAME"></a>
Links to that target location from elsewhere in the document

Formatting

<p></p>
Creates a new paragraph

<p align=?>
Aligns a paragraph to the left, right, or center

<br>
Inserts a line break

<blockquote> </blockquote>
Indents text from both sides

<ol></ol>
Creates a numbered list

<li></li>
Precedes each list item, and adds a number

<ul></ul>
Creates a bulleted list

Graphical Elements

<img src="name">
Adds an image

<img src="name" align=? border=?>
Aligns an image: left, right, center; bottom, top, middle; size sets size of border in pixels

<hr>
Inserts a horizontal line

<hr size=?>
Sets size (thickness) of horizontal line

<hr width=?>
Sets width of rule, in percentage of page width

Tables

<table></table>
Creates a table

<tr></tr>
Sets off each row in a table

<td></td>
Sets off each cell in a row

<th></th>
Sets off the table header (a normal cell with bold, centered text)

Table Attributes

<table border=#>
Sets width of border around table cells

<table cellspacing=#>
Sets amount of space between table cells

<table cellpadding=#>
Sets amount of space between a cell's border and its contents

<table width=# or %>
Sets width of table — in pixels or as a percentage of document width

<tr align=?> or <td align=?>
Sets alignment for cell(s) (left, center, or right)

<tr valign=?> or <td valign=?>
Sets vertical alignment for cell(s) (top, middle, or bottom)

<td colspan=#>
Sets number of columns a cell should span

<td rowspan=#>
Sets number of rows a cell should span (default=1)

<td nowrap>
Prevents the lines within a cell from being broken to fit

Forms

For functional forms, you'll have to run a CGI script. The HTML just creates the appearance of a form.

<form></form>
Creates all forms

<select multiple name="NAME" size=?></select>
Creates a scrolling menu. Size sets the number of menu items visible before you need to scroll.

<option>
Sets off each menu item

<select name="NAME"></select>
Creates a pulldown menu

<option>
Sets off each menu item

<textarea name="NAME" cols=40 rows=8></textarea>
Creates a text box area. Columns set the width; rows set the height.

<input type="checkbox" name="NAME">
Creates a checkbox. Text follows tag.

<input type="radio" name="NAME" value="x">
Creates a radio button. Text follows tag

<input type=text name="foo" size=20>
Creates a one-line text area. Size sets length, in characters.

<input type="submit" value="NAME">
Creates a Submit button

<input type="image" border=0 name="NAME" src="name.gif">
Creates a Submit button using an image

<input type="reset">
Creates a Reset button