How to make a random World generator?

At first, i have to say, that i'm german. Please get not angry about my Bad grammar skills.

My question is: how do i make an algorithm that automatically creates my 2d World (place random trees or something like that). It should spawn them with a biom-based system. And if it goes out of them window it should be saved for the next time if i'm coming back. It should work a bit like the minecraft world generation system, if somebody knows that. Thank you for your Help.

This is a complicated, multi-faceted question that you aren't going to get one simple answer to. You need to research how procedural generation is done as there are many approaches.

For biomes/minecraft style generation here is a good breakdown of the concepts: procjam.com/tutorials/en/ooze

While it's not biome based, Rex does provide some dungeon generation:

c2rexplugins.weebly.com/map.html

You may want to consider Seed generation as well, that tutorial link above covers it a bit, just know that there are Construct2 plugins that can "freeze" your seed so that you always generate the same terrain.

You'll also need to look into how to store the terrain your generator built, probably by writing to an Array object.