Click the Export button (the orange play icon or the "Export" tab). Because you are using "Copy" mode, joining these two segments will happen instantly. The software will not re-encode.
Lossless Cut is the gold standard for portable video trimming. Despite the "cut" in its name, it also supports joining multiple segments. free video cutter joiner portable
FFmpeg is a command-line tool. While not a GUI, it is the engine behind most cutters. You can copy ffmpeg.exe to a USB drive and use batch scripts to cut ( -ss and -to flags) and join ( concat demuxer) video instantly. Click the Export button (the orange play icon