To make sure you have the details you need when you need them, you will need to decide on a system to manage your references. For many students, especially for undergraduate assignments, the easiest way is to set up a Bibliography file that you can keep adding details to as you read. Saving it somewhere you can access it easily from a variety of devices is a good idea - in Google Docs, or Dropbox, for instance.
If you are collecting a lot of references, you might find it easier to use reference management software like EndNote, Zotero or Mendeley. Be aware that any reference management program is only as good as the information you give it! So before you start using any program, it's important to make sure you have a clear understanding of the type of information you need to include and where you need to put it. If it's in the wrong place, or it's the wrong or inaccurate information, the program will not correct it, and it may be more difficult to put right later.