Web parts allow the user to customize their site through a browser.  To add a web part to a site first select SITE ACTIONS and then EDIT PAGE.  Now you should see the Web Part Zones that are on the page; web parts can only be added to web part zones.  Then simply click Add a Web Part in the zone where you would like to put your web part.  A second window will appear allowing you to choose the web part you would like to insert.  You can choose to have data to be pulled from lists, libraries, or any other content on your site. 

Once you insert a web part select EDIT in the top right corner of the web part and then click MODIFY SHARED WEB PART.  This will bring up a toolbar on the right hand side of the browser.  The first section deals with the view, and if you have already created the view you would like to use then select it from the drop down menu, otherwise click EDIT THE CURRENT VIEW.  This will allow you to change the view for this web part only.  The next option in the Modify Shared Web Part toolbar is for the toolbar.  A full toolbar will give access to all of the options available for that list or library.  The next section is Appearance where you can edit the title and size of the web part.  The Chrome Type will allow you to hide the title and/or border, if you choose.  The Layout section can change alignment as well as what zone the part appears in.  The Advanced section has many miscellaneous options that offer even more customization.  When you are done select ok and you should return to the main screen with your updated web part.