How do I make a dip?

Say I wanted to make a bath, how do you make it so it dips like a bath (so its hollow but its also round) and how do you cut a circle into something for say a bird house, how do you cut into it??? anyone please?

not sure what you’re i understand
are you asking how to model a bird bath, if yes this will help

what do you mean by cut into it

Yeah cut into it thanks, this should help

didn’t help, I need to know how to cut into things!!!

You need to be much clearer with your question.
Give an example, screenshots, diagrams, example blend files etc. Your question as put could mean a number of different things. Being precise stops wasting other users precious time en effort
There is the boolean modifier

In a bath it has the outside shell and the inside which is a curved dip. I am wondering how to get a cube and make a sought of round dip to make it look like a bath, I know you can press e (execude) and push it in but thats pushing it in a square/rectangle I am wanting to push in a oval/circle.

You’re better off modeling it round from the start, like in the video above. From a finely subdivided flat surface (like on a cube), you can go into Edit mode, switch to Proportion Editing, change the fall off to Sphere, then grab the center point and drag it down (using the mouse wheel to adjust the size of the effect). However, starting from a rectangular topology, it’ll probably take a bit of manual work to get the edges to be sharply defined.