How to create an SSH/telnet user with read-only permissions ?

I want to allow a telnet/SSH user to peek into my system but have no write permissions.

In other words he should be able to e.g. perform:

ls
find
transfer files from the system
cat

Ok, I could add an user with useradd command.

But then: How can I apply the non-write (=read-only) permission to him ?

And additionally: Assuem the same situation as above but the user should get now
write permissions to the folder /user/home/myuser123/

Peter