First,
You’ll obviously need to download a copy of FormHelper
Secondly, build a new template where you will link to from entries in another template.
You’ll find full documentation on how to do this in the FormHelper plugin, but I’ll provide a basic template below.
<div class="editform">
{exp:weblog:entries rdf="off" show_future_entries="yes" show_expired="yes"}
{exp:weblog:entry_form weblog="my_weblog" return="template_group/template"}
<input type="hidden" name="entry_id" value="{entry_id}" />
<input type="hidden" name="allow_comments" value="n" />
<input type="hidden" name="allow_trackbacks" value="n" />
<input type='hidden' name='dst_enabled' value='y' />
<input type="hidden" name="status" value="{status}" />
<input type="hidden" name="author_id" value="{author_id}" />
{categories}<input type="hidden" id="category[]" name="category[]" value="{category_id}" />{/categories}
<input name="entry_date" type="hidden" value="{entry_date format='%Y-%m-%d %g:%i %A'}" maxlength="23" />
<input type="hidden" name="url_title" id='url_title' value="{url_title}" size="50" maxlength="75" />
<input type="hidden" name="{exp:form_helper:field_grabber field_name='body' which='format'}" value="xhtml" />
<p><label for="form_title">Title</label><br /><input type="text" name="title" value="{title}" id="form_title" maxlength="150" /></p>
<p><label for="form_desc">Description</label><br /><textarea name="{exp:form_helper:field_grabber field_name="body"}" id="form_desc" rows="10" cols="10">
{exp:form_helper:field_parser parse=""}{body}{/exp:form_helper:field_parser}</textarea></p>
<p><label for="form_favoritecolor">Favorite Colour</label><br /><textarea name="{exp:form_helper:field_grabber field_name="favoritecolor"}" id="form_favoritecolor" rows="10" cols="10">
{exp:form_helper:field_parser parse=""}{favoritecolor}{/exp:form_helper:field_parser}</textarea></p>
<p><input type="submit" name="submit" value=" Submit " class="submit" /></p>
{/exp:weblog:entry_form}
{/exp:weblog:entries}
</div>
As you can see, FormHelper makes it a little easier whereas you can specify the “short_name” of the field…
I’ve also set my Categories to show as hidden… you can populate them as a dropdown like this:
<select multiple name="category[]">
{exp:form_helper:categories entry_id="{entry_id}" parent_id="1"}
<option value="{cat_id}" {checked}>{cat_name}</option>
{/exp:form_helper:categories}
</select>
The key thing is to have a Weblog Entries loop wrapped around the form and have the form linked to dynamically so that the data is populated.
You can easily make links to the Edit form by putting code like this on your frotn end templates (within the weblog:entries loop):
{if logged_in_group_id == "1" || logged_in_group_id == "6"}<a href="{permalink='path_to/edit_form'}">Edit Entry</a>{/if}
The code above allows for both Group ID #1 and #6 to see a link that will set itself to the Edit Form 
