Video Editing Software

Although there are differences between video editors, many have the same basic functionality of "gathering your ingredients" and putting them together. 

Free online tools

Both of these tools leave what's called a "watermark" on the video. A watermark is often a logo. You can think of it as free advertising - in exchange for letting you use their tool for free, your video has a small logo that acts as an announcement of the software you used to make your video.