Yes it can. Where are you running into problems? The basic process is going to be:
1. Import your greenscreen footage and place it on the timeline.
2. Apply a key to the footage and adjust the settings as necessary.
3. Import your background and add it to the timeline below the greenscreen footage (unless you want a black background. For black, skip this step).
4. Grade your footage to eliminate all color and create the silhouette.
The video tutorials here
will explain basics of keying, masking, and key grading if you aren't familiar with the basics there. Id also recommend taking the time to watch the Interface tutorials on that page, to get up to speed on the fundamentals of using the program. If there is a particular step that is causing you trouble, let us know and we can offer further assistance. If it is the key itself that is giving you trouble, we will need to see either an image or a clip of the footage at full resolution to offer more specific advice.