If it comes in liquid form, you can inject it as is.
If it's a powder you have to mix it with injection suitable water, either Sodium Chloride or Bactrriostatic Water.
Normally peptides are made and lyophilized, or "freeze dried". This makes it into a stable powder that can be stored almost indefinitely.
There are also concerns that some liquid peptides can degrade in heat (>10C), can be damaged if shaken or otherwise mishandled. Freeze drying eliminates these concerns.
I've not seen a supplier provide a liquid form for quite some time. I'd also have precautions in AUS due to the heat. MT2 is generally quite strong and can resist heat, but that doesn't mean all peptides will.