I've explored free online dating sites as a way to "have a look around" among so many dating websites. I'd suggest you to do the same if you want to start using internet dating sites and see how things work. Most dating sites offer free registration, you can create your profile and view other members' profiles but if you want to contact someone you have to pay for a subscription. Read more on how Internet dating sites work.
A few are really totally free dating sites. That is their main advantage and usually they have a lot of members. On the other hand, the disadvantage I've seen is that anyone can register, create a profile and contact anyone else, so a lot of people do not put much effort into it. A lot of profiles I saw (especially of men) were boring, saying nothing about themselves and what they wanted. How can you choose someone? So if you decide to use free online dating sites, don't make the same mistake, write an attractive profile. Read a few tips on writing a dating profile.
On free on-line dating websites you can find all sort of people, who are looking for any type of relationship, from nothing serious to friendship, to marriage and many people state they are interested in all of these types of relationship. So, it's like trying to find the proverbial needle in a haystack.
If you wish to have a look, the biggest free dating site is www.plentyoffish.com where you can select people by interests and characteristics. Also www.okcupid.com is good, with a lot of criteria to select people. I've found another one in UK www.completelyfreedating.co.uk
However, if you are dating for a baby, to find a partner to have children, I don't think free online dating sites are the best place to start because it's difficult to select members based on their intention.
You'd be better off with some targeted websites, also called niche websites, that select people based on their interests and lifestyles (religion, race, sport, politics, etc.) and where you can find someone with the same interests as you have. For examples, there are for Christian, Jewish, Muslims, Russians, Indians, Latinos, pet lovers, vegetarians, etc. Just type in a search engine what you'd like to find.
Most of them are paid websites, but I've found a whole network of free targeted websites, a very good idea, have a look at www.passionsnetwork.com.
Other website target specific relationship intent, like adult dating, dating for marriage, no commitment so you know it from the beginning and don't waste your time.
I very much prefer meeting new people in person. I find going through a lot of dating profiles quite depressing, most of them are so terribly boring!