I am trying to add another activity to my project but it seems like the options for that are greyed out
Here's what it looks like to me:
You need to change your minimum SDK level. That's why it's greyed out - yours is set to be too low.
AndroidManifest.xml, right under
<manifest . . . >, add this:
uses-sdk android:minSdkVersion="15" />
You can change the value there to any value...you only really need 8 or higher for most of the activities you are trying to add.