Have you done any smoking / grill work before? Be advised than a smoker with an offset firebox, using wood, is the most difficult of all grill to use.
Hard to keep at a stable temperature due to the offset nature, and little insulation on the grill section. Can lead to wide fluctuations in temperature as the beginner is always over-reacting to the grill temperature. That said, that style is tops for briskets and other items where you want a full bark on them.
Couple of tips:
Cooking is temperature based, not time. Using time is like saying drive 45 minutes and turn left, instead of drive 45 miles. If you don't have one, buy a good digital temperature probe for the meat, and with an offset smoker, for the grill temperature, as the little metal arrow on the door might as well say cold, warm, and hot, on it, as accurate as they are.
Get a probe that you can connect to your phone, so you can look at a graph of temperature compared to time, to see what's happening to the meat - cooking at a steady pace, stalling, coming out of the stall, etc. It gives you heads up on what's happening.
Brisket is the hardest thing to cook - try pork shoulders first. With much more fat, and more tender meat, they are much more foregoing than a brisket for starters.
I'd practice with charcoal before I used wood as my primary fuel source. As above, the offset smokers are tricky to keep at the same temperature for a beginner - even harder if you're using wood of varying size, quality, compared to charcoal.
Let us know how it goes. Good luck.