Hi @asmaa_ali and welcome to the MongoDB community forums. 
The mongo tool is not distributed with MongoDB version 6.0. If you recently installed/upgraded to MongoDB 6.0 this is why you get the message.
In your original screen shot you had connected to a database using the mongosh tool (this replaces the older mongo tool). However you were then trying to run commands such as mongodump and mongoexport inside of the shell and that won’t work. These commands are meant to be run from your terminal/command prompt. The mongosh is an interactive shell to run queries against the data in your database. mongodump, mongoexport, etc are other tools that allow you copy your data from one server to another.
If you haven’t done so already, you might want to take the M001: MongoDB Basics course.