The Race tab is where you select your race (you can only have 1!), and where you can pick any templates that apply to your character.
Sort Races (Drop Down Menu) - There are 3 ways you can categorize the Races: By Name (no hierarchy), By Type (the Types of races are the top-level, with races of that type being listed in it), and By Source (as in books that were loaded in the Source Material tab)
Selected Race (Information Reporting) - This indicates what Race you've selected. It will display <none selected> if no race has been selected.
Select (Button) - To select a race, you can double-click on it, or you can click on it and then click on the Select button.
Upper Left Frame (Tree Window) - This table lists the available races. You can filter what races are listed by clickin on the filter icon (the magnifying glass icon in the toolbar). The table will display various attributes of the races, and you can sort by those columns by clicking on the column header. Races which you don't qualify for will be shaded with the pre-requsite failure color (default is red). In the Pre-Reqs column the pre-requisites for the race (if any) will be listed, with any pre-reqs that you don't meet being shown in the pre-requisites failure color.
Race Info Frame (Information Reporting) - This displays the details of the race you last clicked on.
Available Templates (Lower Left Frame) - This table lists details about the templates which are currently available in the sources you loaded. PCGen is meant to handle "permanent" adjustments, not situational ones. Some users have created templates to handle situational modifiers (like Rage) in order to produce a character sheet with the adjustments for that template calculated into the character. To add a template click on one you qualify for (the Q for Qualified column has a Y in it) and then click on the right-arrow button.
Selected Templates (Lower Right Frame) - This table lists all the templates the character currently has, including whether or not the character can voluntarily remove the template or not. Removable templates can be removed by clicking on them and then clicking on the left-arrow button.