Good Morning Dstelley
Driving a steam locomotive takes quite a bit of practice, so don't despair
The first thing is that you need to change your 'firing' style to suit the conditions. You should be pre-planning ahead (how long you need to pre-plan depends on the locomotive).
When working the locomotive hard, you should have your 'coal level' at around 100% (this is optimum, giving the hottest fire), and your water level at around 70-80% (this allows you to put a bit more in if making too much steam, or allow it to use some up before turning the injector on again).
According to your screenshot, you've got 100% water and 147% coal in the locomotive. Essentially you've got too much water in the boiler, and not enough steam space. And too much coal, and have essentially smothered the fire. You could recover this over time, but it will take quite a white to get it hot and stay that way, then raise pressure. If you want to try this...
First, turn the blower onto full. To work out which control is the blower, go into the cab view and hit N and Shift+N (this one turns the blower off) a few times, and look for the moving cab control.
Next, walk away for a while (or drive another train). Check on it every 5-10 minutes. Note, let the boiler actually reach full pressure. Turn the blower down at this point, and then keep the fire at about 70-100% if you're going to start working the loco hard, otherwise just leave the fire to burn down a little (anything down to about 50% is fine on the Berkshires). If the boiler is over-filled a little (the water level can go beyond 100%; this value simply shows the amount of water in the gauge glass), then you'll need to let the loco blow off the safety valves for a while (technically you'd use the blow down to lower the water level; but Trainz doesn't support this at this time).
Regards
