Need help with my slant six

Okay guys you are going to have to bear with me. I am only 17 and I still have a lot to learn but hey thats what you guys are for right? Okay so I pulled my 71 demon outta the shed yesterday and it started up great. I drove it the 10 miles home parked it outside and shut it off. Now today it will not start for me. It cranks and turns over and seems like its gonna start but dies a second or two afterwards. I do not really know where to even start. I do know that it is getting fuel so its not that. Can anybody help me out? (Its got a 225 slant six in it)