Answer: Photopea allows you to open multiple documents (e.g. JPG images) at the same time. The list of opened documents is shown in the bar at the top of the main area. Here you can switch between documents and choose the one that you want to work with.
The Zoom Tool is used to change the zoom level of your working image. If you only click on the image, the zoom is applied to the whole image. But you can also click-and-drag the mouse pointer to create a zoom rectangle.
Layer opacity. You can control the opacity for almost every layer in a Photoshop document. The opacity determines how transparent or opaque the layer will be. In other words, it controls how much the layers below can show through. Take a look at the example below.
Change layer opacity – in the Layers menu, tap with two fingers on the layer you want to change opacity. The Layers menu should close and you can slide your finger or pen anywhere on the screen left to right to adjust the opacity. You should see the opacity near the top of the screen.