Connect the device containing your MTS files to your computer. Click the "Start" menu in the lower left-hand corner of the screen and choose "Computer" or "My Computer" from the menu options. This opens a window showing all the devices connected to your computer. Verify that the device you connected shows up in this section.
Adobe Premiere CS5, the current version as of 2011, recognizes the MTS file extension associated with the AVCHD video format. You can import these files into Premiere and edit them in the timeline with no special modifications. However, because of licensing restrictions, you need the full version of Premiere. According to Adobe, the trial version of the software does not support files with the MTS extension.
Click "File" from the menu at the top of the screen in Premiere and select "Import." This opens a window that allows you to navigate to any file in your system. Locate the MTS file you want to work with and double-click it. After a few seconds, the file appears in the project panel. This is the upper left-hand panel.
Click the file and drag it to the new item icon. This icon is at the bottom of the project window between the folder and the trashcan icons. It appears as a sheet of paper with a folded corner. The clip appears in two places. First, it is in the monitor panel at the far right of the screen. This shows a preview of the clip. It is also in the timeline panel below and to the right of the project panel. In the timeline, the clip consists of two bars, with the top bar representing the video portion of the clip and the lower bar representing its audio portion. Here, you can select any tool you want from the toolbox to the right of the timeline, or drag the clip into the panel to the left of the monitor panel. Here you can apply visual effects and adjust the audio.