A classic Terran opening. While playing TvP you should master this Build Order that allows you to start up economically while having the possibility of harassing your opponent. Over the course of this guide we will have a look at the different follow-ups for your 1-Rax-Expo. Played very often by the professionals, this Build Order offers you different options when opening.
Supply Depot
Barracks
Marine
Orbital Command
Command Centre
Supply Depot
Marine 
Bunker
Barracks x2
Refinery x2
Orbital Command (expand)
At 100% Barracks, build a Tech Lab
At 100 additional gas, build a Factory 
Build a 1 Reactor + 2nd Tech Lab on the Barracks - start production of the Marauders
** the numbers 10/12/15... refer to your population in the game **
***Similarly, don't stop your production of SCVs!***
Generally with the 1-Rax-Expo you can take the pressure from the Protoss with your Marines. For example, four Marines per Stalker will be enough to hold in the early-game. Nevertheless remain vigilant as you remain vulnerable to a 4-Gate Rush. In summary, place one or two Bunkers if you feel your opponent will quickly attack you. Also be careful with your first units and wait for your first Marauders and your Stimpack.
As I said this is a very "standard" strategy so Protoss will expect you to choose a stranger strategy like a double Command Center or something, you will have to make good decisions if you don't want to get surprised.
Note that you have other follow up possibilities other than building your three Barracks :
Your gas allows you to start a Factory more quickly and send out Siege Tanks either to defend or attack your opponent at a specific time. The construction of several Barracks without taking gas will let you push (6 mins) very aggressively with a lot of Marines that can surprise your opponent.
Take another base directly after placing your expand (B2) based on what you have scouted.
