In Brethren RaidFrames, Raid Templates and Frame Styles dictate how players are organized and shown to the user (you). Raid Templates are how players are grouped together. Where as Frame Styles are how the individual players are displayed.
Rain Templates dictate how players are grouped together on the screen. Each Raid Template has its own intended purpose and layout, I will go over each of the predefined templates.

This template sorted players based on their role in the raid. Players are placed into the following roles: Healers, Ranged DPS, Melee DPS, Tanks, and your party. There are 5 windows in this template by default. This style is useful if you are in charge of healing a specific role or you would just like to have it separated for logistical reasons. All windows can be un docked and moved around as desired.
To learn how to add and remove people from the different roles, see Player Roles

This template splits players into their respective group's window. This template is probably the most used template for obvious reasons. All windows can be un docked and moved around as desired. Groups 1-5 are shown by default.

This template shows the whole raid in a single window. The window grows vertically and then horizontally with a max of 5 rows. This was primarily made for users who use the grid Frame Style.
The window looks at the raid as a whole, if there are 3 people in group 1, players from group 2 will fill in the last 2 rows of the fist column.
Frame Styles are how each individual player is viewed by you. They are the bread and butter of any raid healing mod so a lot of time and effort has been put into these styles to provide the information you need, give familiarity to those who are new to RDX, and to try and set them above the rest with special features such as hot bars, boss bars/highlights, and the mini dispel grid. You can change many aspects of these styles with the Frame Settings window. I will go over each of the five Frame Styles.

The default style is the only style to support the mini dispel grid and is my personal preferred style. The boss debuff bas is displayed along the top, hots along the bottom. Buffs hidden by default.

Designed to help people migrate over to RDX this frame is a decent clone of the sRaidFrames style. The boss debuff bar runs along the top and the hot bar runs right below the name. Show buffs if no debuffs is default for this frame.

Designed to help people migrate over to RDX this frame is a decent clone of the perfectRaid style, though the ability to move the name to the right has not yet been implemented. The boss debuff bar is displayed along the top and the hot bar runs along the bottom.

Designed to help people migrate over to RDX this frame is a decent clone of the grid style It even has the four corner boxes that light up for various reasons. The healthbar moves up and down, and the name will turn into the amount of missing health once the player has lost 15% of their life. The outline of the box will turn white if the player is in need of healing (< 70% life). The outline will also change color for agro(red) and various other colors for spell debuffs. The outline will only change to a spell debuff color if you can dispel it. The boss debuff bar is along the top and the hot bar is along the bottom. The four corners are as follows:
Turns red if the player has Agro.
Turns gold if the player has pom.
Turns green if someone is casting a heal on this person.
Turns dark green if there is a hot on this person.