Yes, you can create a Sharepoint list from your spreadsheet. As for adding more fields, you can do it before or after you import the spreadsheet. I'd probably do it beforehand in Excel. Just add your additional column headings that you need and save the XLS.
To create your Sharepoint list, go the the Site Actions menu on your site and select Create. On the create page you'll find "Import Spreadsheet" under the Custom Lists category. Once you select it step 1 of a 2 step process will appear where you enter the preferred name for your List and specify where the spreadsheet is. Step 2 occurs in Excel after it opens your file. A dialog will be on screen asking you to select the desired range of cells. Be sure to specify a range where the first row is your desired column names. Click OK and in short order you'll have your list.