What skills can prisoners learn in prison?

At present, general prisons and provincial labor departments jointly run vocational training courses, which can obtain corresponding vocational skills certificates, which are as effective as those in society.

My prison provides housekeeping, car maintenance, home appliance maintenance, primary computer operation and so on. ...

But to be honest, these so-called courses are almost all taught by prisoners themselves. As for exams, prisons generally try their best to take care of graduation. So, a certificate is better than water, but it's better than nothing, right?

This is also the helplessness of being a prison policeman. Fake diplomas are still flying all over the society, not to mention prisons.