So you've read through the text contents of the file, and you think you might need to enable those macros. You click the Options button on the Message Bar and the Microsoft Office Security Options dialog box opens, where you can choose to enable them.
The exact choices available in this dialog box will depend on the type of potential security risk identified. As mentioned previously, macros are by far the most likely reason you'll be notified of a security risk in a Microsoft Office file, such as whether the macro is signed or not and whether it's from a trusted publisher.
You can choose to leave the potential security risk disabled, enable the macro (or other code) for just this one occasion, or, if it's signed, trust all code from that publisher. If you trust all code from that publisher, the publisher is added to your trusted publishers list and you won't be asked on a file-by-file basis to make a trust decision for every piece of code from that publisher.
If one file contains multiple macros, your choice will apply to all of the macros — you can't choose to enable one but not the others. However, if a file contains macros and some other type of potential security risks, such as links to external data, you will be presented with a choice for each type of potential security risk and be able to, for example, enable one security risk type but not the others.