Post edited 3:54 pm – September 10, 2015 by MoneyTime
I'm not sure exactly what you mean by freelance writing.
There are sites like TextBroker that you can get paid writing gigs (people post a description of what they want and you can accept it). They pay a range based on the quality of your past writing (ranging from 0.7-5 cents / word). You can work as often or as little as you want with them (as long as you complete all the assignment you accept of course).
Or, you could hang out a shingle and offer to do this sort of work like budgetblonde does (http://www.budgetblonde.com/hire-me/).
Heck, she event offers a course on how to do this - https://gumroad.com/l/write-for-blogs-master-level/budgetblonde#. I'm sure this would cover all your questions.
Or, you could offer to work for a specific site, probably related to your blogging niche. I used to do this on MoneySmartsBlog – I co-owned the blog and had my half bought out by the other owner. He wanted me to keep writing, which I did for $20 / post. He told me I could post as often or as seldom as I wanted on whatever topics I wanted. Eventually we agreed to part ways, and when we announced it I had numerous offers of other writing gigs (which leads me to suspect that you can get more than $20 / post =).
This is almost a blog post ;-P.