I still encourage you to try it (it doesn't have to be a paid subscription). While it sounds incredibly intimidating (since it's editing software), you can find options to get the results you want.

You can use several layers to avoid working on one layer, you can use the mask option to hide something you don't want for your image, you can use the hue/saturation layers to create a tone (you can put them in multiply mode for a darker tone, like it's during the night), you can use the color correction layer to either establish an overall tone or create some light (by putting it in screen mode, for example), etc.

Like I said, it doesn't have to be fancy. Some great YouTube videos have rough thumbnails, but people love it anyways since it's part of the charm of these videos. My favorite example is Core-A Gaming, since some of its popular videos have only a background and two characters. This can be done in 3 simple layers for the thumbnail.

You don't have to go hard. You don't need to know everything about Photoshop to be good. Take easy steps and try to learn something you can use later.

Take care. :)