I am trying to make that type of poster for my science project but i can't find any tutorials related to it.
There's quite a few ways to do that. Here's how I'd probably go about it.
Create your text, then convert them to shapes.
Merge the shape layers.
Select the rectangle shape tool, hold shift and draw a rectangle that's bigger than the canvas. Change it to Exclude Overlapping Shapes (just for the rectangle path).
You now have a shape layer that masks the non-text portion of the image, so you can change it to black (or any colour). Simply place your images or anything else below that layer and it'll appear inside the text.
Another method for achieving something like this would be to use a clipping mask. Depending on exactly what you're after, you may even be able to leave the text editable. Actually, you could convert all the text layers to a Smart Object and use a clipping mask for the images on top. It really depends what you're trying to do and what your criteria is (if the image needs to be scalable to bigger sizes without quality loss).