A Duldung (temporary suspension of deportation) is not an Aufenthaltstitel (residence title). It means that you are required to leave Germany, but you cannot currently be deported for a specific reason. For example, you may have a Duldung because you are seriously ill, you have a minor child in Germany, or you do not have a passport.
The government allows you to stay in Germany as long as this reason applies.
Your Duldung also states whether you are allowed to work. You can find more information here:
Beschäftigungserlaubnis (employment permit)
The Landesamt für Einwanderung (LEA; State Office for Immigration) issues a Duldung if it determines that there is a reason why you cannot currently be deported.
The Duldung is a folding card without a chip.
