Hi welcome to FW! I'm so glad that God directed you here. It sounds like you would have some awesome life stories to share. I can't even begin to wrap my mind around doing what you do. What a wonderful calling that must be. I'm delighted that you feel lead to do some writing now, too. I look forward to reading it.
The challenge is one of the most popular spots here for sure. If you can afford the few dollars a month it is so totally worth it. Each week a new topic is given. If I'm not mistaken the next one is on the word accent. There is a word count limit which has helped me learn to tighten my writing up quite a bit. The deadline has also helped me on my procrastination. I still wait to the last minute but am writing on a more regular basis.
Silver members can enter the challenge four times a year. They also can enter the blogging contest. This month it is about Equipped to Defend. You can find more info on it here
You can also enter your stories under the general submissions. You may want to leave a link here or in the Open Forum so people can find the stories easily.
You also can find a wealth of info on the boards. It's also a great way to make friends. I've become close to people from all over the world. A great place for writing tips can be found at Jan's Writing Basics.
The Critique Circle is a great place for paid members to receive a detailed critique on their work. Just recently, they have allowed members to pay so much a page for detailed feedback. This is for silver members or members who want a critique but don't have the time to critique someone else's work. That's how the circle works. Each time you leave feedback, you receive a credit to allow you to post a piece and to get a constructive critique.
I hope I gave you some places to start. The site is huge and there are so many wonderful things here. You may want to check out the FAQ thread as that may answer many of your questions.
Have fun exploring, jump into conversations and don't be afraid to ask any questions.