Answer:
There are hundreds of dating sites online. The best things to do is research them, compare them, and then decide which ones might suit you best.
One website called Match is considered very good and it has been around for a long time. You need to pay to join but it has a proven track record and advertises in the media, including television, in many countries. With Match, you can meet people from all over the world as well as your own country. There is the option for dating/relationship matches or just friendship matches. There are tips on how to use it and free, optional, compatibility/affinity personality tests if you want to make use of them.
Most people are looking for serious relationships, or dating with a view to developing a serious relationship, not a romp in the hay.
Be careful that whatever dating site you use is not too new. If they are new, they may not have many members
There are a few free dating websites. Some options are PlentyOfFish, 2meet4free, OK Cupid, Matchdoctor, 4single, freeonlinedating, and Craigslist. However, be careful, you may get a lot of spam at the free sites, particularly at Craigslist. You may first want to read up as much as you can about online dating tips and advice.
Watch out, however, if you are going for a free online dating site. You get what you pay for, as the saying goes. It can be wiser to pay a few dollars/pounds/etc, and get better quality and better choices.
Always look for profiles with a photograph. It is a known fact that some people who decline to add a photograph are married and not wanting to be spotted (by people they know) on a dating website.
In addition, always play safe. A good site will advise you how to do this. Never agree to meet anybody too soon. Meet in a public place and never meet a stranger without telling somebody where you are going.
The best online dating site is definitely one that is easy to use, where you can find out a lot about the people on it and where you can post your own information easily. And you want people to be honestly looking for a serious relationship, just like yourself.