This is a question that I get from a lot of first time writers. They have a written book that they have worked over for some time and they are proud of it, as they should be, but they don't know what the next step is. To be honest I don't know the next step, at least not for everyone. Every writers journey is different. There will always be writers who don't make it, sorry but that's reality, and then there are writers who struggle some where in the middle of making it and not making it. Then there are those that defy normality and shoot to the top, passing even their own dreams and expectations. So when you finish your book there is a number of steps you could take.
I would suggest, as I learned the hard way, to go back over your book a few times. Clean it up and then let a few people read it and have them give you HONEST input. Don't hand it to someone who doesn't read your genre and expect a true review of the novel, they don't have the experience in the field to give you a good idea of the strengths and faults in your work. After that its all up to you. If you want to try the traditional publishing route their are outlets for that, finding an agent ect. ect. Its really easy to google that and find a list of agents who are looking for potential writers. I would recommend that if you decide to go that route do your homework. Figure out how to properly write a query letter and find agents who are looking for you. I have seen so many writers get discouraged because they get 20 rejection letters in the mail but they are sending their religious inspiration novel to agents who represent erotica. Of course they are going to reject you. Do your homework and go at it properly, you will only get out of it what you put in it.
If you are wanting to go the route of an indie writer or self publisher then that route branches off to hundreds of other routes because now the work that would be done by an entire team of professionals now has to be handled and done by you and you alone in most cases, unless you pay a couple of thousand dollars to have a similar team work on it. Again the key to success in that field is to do your homework. Put the time and effort into a website, a blog, the COVER of your book. The more you put into it the more you will get out of it.
There is so much more in this that I could write pages about this topic. If you have any direct questions please feel free to leave them in the comments and I will be sure to get back with you.