There are several search engines on the web to choose from. www.Google.com is one example, www.Dogpile.com and www.Ask.com are a couple more. Whichever search engine you choose, open that search engine webpage.
Type a lyric fragment into the search engine. Don't type in all of the lyric fragments—this will cause too many results. Rather, type in the most complete line of lyrics you can remember and add "+ lyrics." Then click on the "search web" button or "search" button.
The results will most likely contain the song you've been looking for. If none of the results match, try going back to the original search engine and typing in a different set of fragments.
Another option, if the web isn't helpful, is to call the local radio station that specializes in playing the type of music that the particular song is grouped in. Is it a rock song? Call the rock-n-roll radio station. For a country song, call the local country station, and so on. They'll likely know which song it is. The phone numbers for these stations can usually be found using the search engines—simply type, "(name of station) phone number" into the search engine and a list of local businesses should appear, matching your search.
If the lyrics sound familiar to you, and you think they may be written by a specific band or singer, you could try typing the singer or band's name into the search engine, as well as a few of the lyric fragments. This added information may increase your chances of finding the song you're looking for.