Please take some time to look everywhere to see what forums we have for specific questions.
In this the user gallery forum you will find the answers to your questions since it has been asked many time.
This is the most common reason users have problems.
Size- if the picture measurements are too large you will see error message on the next page after trying to upload from your CPU that will tell what is wrong with the picture you tried to upload. Either the measurements or the actual picture size on disk.
Where do I have the option? -Where it has 5 "browse" boxes is where you select your picture from hardrive. After you have the pics selected, just choose upload. If you see an error message refer to size above.
320 Mega Bytes for disk size and 750 pixels in width, I believe are the maximum for pics. Don't know the height max though, never had an issue.