Put the pictures for the GIF into a folder. Name this folder to prevent any mix ups with other pictures on your computer.
Open Photoshop CS5 and create a new project. Adjust the dimensions of the canvas to match the dimensions of the pictures to be used in the GIF.
Create new layers. Make sure each picture for the GIF has its own layer. Click and drag the pictures into Photoshop being sure to place each picture into a layer. Rearrange the pictures by clicking and dragging the layers until they are in the desired order.
Click Window and select Animation to open the Animation palette. Select the menu for this palette and click Make Frames From Layers. The frames should be shown as individual thumbnails in the Animation palette.
Click the black downwards pointing arrow below the frames to select how long each frame has in the overall animation. Below them is another place where you can select how long this animation will loop.
Click File, then Save for Web & Devices. Select the file format for .GIF and save.