It takes a special kind of person to deal with the homeless population. This group is a hard group to crack. They do not trust motives and always seem to look for the opportunity to say "I knew it" when something does not go their way. The true successes are rare, but they are worth the time and effort.
Become a nonprofit organization. If you want to create a charity for the homeless, most likely you will be a 501(c)(3) organization. That will take a little bit of time and at least a couple of thousand dollars if you use an attorney. It requires a board, articles of incorporation, and some type of proof that you are not looking to make a profit so that you can be qualified to be tax exempt. If you are going to be doing lobbying, then a 501(c)(3) is not for you. Consult an attorney for the correct structure for what you want to do.
Decide how you will give assistance. There are so many ways to help the homeless, so you should make sure that you are not just duplicating a service. Find out what the needs are in the area you want to serve. Do they need food, help finding housing, emergency shelter or a place to hang out during the day? Depending on which one you choose, the money you will need to raise will vary.
Start small. With the homeless, it is all about relationships and feeling like they are being cared for. Too many have experienced the wrath of people who serve the homeless despite their disdain for them. Unfortunately, some of the worst are former homeless individuals.
Be consistent. If you say you are going to be out there serving food from 5:00 a.m. to 7:00 p.m., then the homeless will be waiting for you. If you don't show, then they will not believe anything you say, and that could put any future endeavors at risk. When you get a reputation for something negative, it is difficult to overcome.
Raise donations from various sources. One of the worst mistakes that some charities make is relying on one source for all their income, particularly a government agency. If you don't get a contract or lose one, and don't have another source for funds, then your work is over. Build relationships in the community; involve them in helping you.