Rek1t

The 'USB Boot Prep' tool let's you prepare your USB stick so that you can install Windows Vista/7 from it, your computer does require support to boot from USB for the USB stick to work.
Caution: The 'Full (Format)' button will format everything on the USB stick. W7T will ask if you're sure though.

Yellow: Usually means it is RAW and has not been formatted, not bootable.
Green: This means the drive is already bootable.
Step 1: Plug in your USB stick
This tool won't work without a USB Stick so go ahead and insert one.
Step 2: Select your stick
Hopefully W7T will detect your stick and list it, select the disk/partition you want to be bootable and click start.
Step 3: Select Quick or Full
Quick: This will just mark the partition as 'Active' and convert it to NTFS if needed.
Full: This will 'Clean' the USB stick remove all partitions and data.
W7T will work it's magic and let you know when it's done, once done you just need to copy and paste your installation files onto the USB stick.

You can think of WIM Manager as a GUI version of DISM/Imagex. You can rename, mount, unmount, delete, import, export, integrate unattended file, and so on...
NOTE: If you plan you on integrating stuff you don't have to mount it via this tool first, you can just go straight to All-In-One Tool.

1. You will probably see an empty list unless you have select an image before, if it's empty then go to 'Browse' and select the following option:
a) If you have extracted an ISO or copied the DVD onto your HDD then select the 'extracted DVD' solution and select the folder root (not the 'sources' folder itself but the folder before that). i.e. C:\\Win7SP1\\
Select a specific wim. Useful if you want to select the boot.wim or if you just have the install.wim without the other DVD contents.
OK, once done, you should see a list of images and a bunch of options.

Apply Unattended

If you created an unattended file then you can integrate it here, just simply select your unattended file.
Delete Image

This will literally delete the image from the install.wim, it is recommended to rebuild the image after you have delete all of the images you needed to delete, but you can rebuild just before you close WIM Manager (so you only rebuild once).
Edit

This lets you edit the name and/or description of the selected image.
Export

This lets you export the select image to its own *.wim file, can come in handy.
Import

This lets you capture a new image to add to the currently selected install.wim. This uses the 'Capture Image' tool.
Make ISO

Makes your selected DVD/Folder into a bootable DVD!
Merge Image

This lets you merge another *.wim into your selected install.wim, for example you can add your Vista into your selected Windows 7 image to create an All-In-One.
Mount Image

Self-explanatory, lets you mount the image.
Rebuild Image

This is probably the most handy feature, if you have made loads of edits to your image like integrate updates, delete files, then i recommend you do this as it will decrease the size of your install.wim which makes your ISO smaller.
Already Mounted Image

If you have an image already mounted it will be displayed like this. You can actually switch to the All-In-One Integrator and select this image to work with.

Set Product Key

This uses DISM to set a product key for the image.
Unmount

Unmounts the image, asking you if you want to save or discard changes.
Other Tools
This lets you switch between tools and save you from going back to the Tools Manager and selecting the new tool.