The MMEL is for things that happen before an aircraft blocks out. Once you blocked out you should refer to the QRH. If an item is listed in the MMEL and not the QRH then use the MMEL M and O procedures.
If you use the MMEL you must comply with any M and O procedures. If you can safely continue the flight with the operatinal limitations (fly at a lower atlitude for example) imposed by the MMEL then you can continue the flight. If you cannot comply with the limitations and continue the flight you must come up with another plan.
If you have a problem in flight then you run the QRH and comply with any operational limitations it may impose (fly at a lower attitude for example). The QRH will tell you if you need to land as soon as practical or land as soon as possible. If the QRH does not tell you to land then it is up to your judgement whether to continue the flight or make a new plan.
Once you land after using the QRH then you will either have to have the equipment repaired or deferred per the MMEL.
If you use the MMEL you must comply with any M and O procedures. If you can safely continue the flight with the operatinal limitations (fly at a lower atlitude for example) imposed by the MMEL then you can continue the flight. If you cannot comply with the limitations and continue the flight you must come up with another plan.
If you have a problem in flight then you run the QRH and comply with any operational limitations it may impose (fly at a lower attitude for example). The QRH will tell you if you need to land as soon as practical or land as soon as possible. If the QRH does not tell you to land then it is up to your judgement whether to continue the flight or make a new plan.
Once you land after using the QRH then you will either have to have the equipment repaired or deferred per the MMEL.