Premiere Pro is a proprietary video editing program maintained and owned by Adobe Systems. Premiere can be subscribed to by itself or part of the larger Adobe Creative Cloud package.
Most computers on campus have Adobe Premiere installed. When you run the program, it will ask for your MyLoneStar username and password. If you have trouble launching or logging into Premiere on a campus computer, quit the application and launch the Adobe Creative Cloud application. Once you have logged into Creative Cloud, you should be able to launch Premiere without issue.
For home use, students can get a student subscription through Adobe: https://www.adobe.com/creativecloud/buy/students.html
If you are saving this to a USB, make sure copies of the video and images that you'll be working with are save on there as well.
You can adjust the length of a clip by positioning the cursor at the end of the clip. It will turn into a red bracket. You can then drag the clip to adjust it's length.
You can also use the razor tool to cut a segment into two pieces. Select the razor tool and then position it where you want to split the segment. You can make several cuts to the same segment, and then use the selection to move or delete them.
The razor tool is good for when you need to trim a section out of the middle of a clip.