Remember to save your work often. Saving frequently lessens the risk of losing the work you have been doing. To save your Photoshop document, do the following:
NOTE: If you save your file as PSD (default Photoshop saving format) your layers will be preserved, but the file size will be large. If you save your file as JPEG (a common image format) your layers will be flattened and become one layer, and the file size will be significantly smaller.