Are you investigating the whole 'prepper' or 'survivalist' thing? Here are some steps to get you stared...
Chances are that you already have a threat in mind, but there are many different threats. Some are man-made. Some are natural. Some have high possibilities, like a massive solar flare once every 150 years. Some have low possibilities, like a large asteroid impacting the earth every 5,200 years. Some will result in the complete collapse of society. Some will result in temporary unrest. Knowing the potential threats will point you in the right direction and give you an idea of what to prepare for.
Who will you survive with? Where will you meet? Where will you go? You should have a plan for every scenario you are preparing for. Different scenarios will require different reactionary plans.
Based on your research, you should begin compiling a list of supplies you might need. Your list will be influenced by things like, is it for long-term or short-term, will you bug-out or stay at home, and if you bug out, in what climate and terrain will you be. Here is a good list of supplies for long-term survival in North America.
Reorder those supplies by value-to-price and begin buying those items in order. You can increase your survival chances to 50% by just spending $100 and having a moderate level of survival knowledge. However, if you want to survive and be reasonably comfortable, you'll want to spend $3,000 or more.
Begin learning any kind of survival skills that will help you, such as procuring water and food, first aid, medical, dental, shelter construction, defensive tactics, tactical operations, communications, raising animals, etc. As you learn, do trial runs and spend some time training. You can do things like begin a garden and do mock bug-outs. Most likely you have other preppers in your area with whom you can connect. Learn from them and train with them.