Marine, Marauder, Medvac is a very common Terran strategy. MMM can move reletivly quickly compared to Terran mech. It also allows for attacks on multiple fronts.
Basic Build order:
1. Get 10 SCV cap, then make supply depot.
2. Continue to make SCV, then on 12 cap, go with Barracks, and do non-stop scv pump. Also get gas and have the orbital command after the barrack is built.
3. On 16 Cap, build your 2nd depot, then put tech lab on your barrack, then pump out those marauders
4. Build the second barrack, get the MULE when orbital command is done, and produce reactor on your 2nd barracks. Pump marines and marauders continuously.
5. You can then build factory, then starport to make medivac, or probably siege tank.
6. When you have the MMM combo, it's time to go for a push on your enemy.
This is just a basic outline of the strategy. It is important to know how to adjust and react to your opponents plan.
Here is a good video explaining it: