The first place that beginning guitarists will turn for beginning acoustic guitar tabs is the Internet, often just doing a search for "Beginning Acoustic Guitar Tabs" or whatever they're looking for at the time.
Make no mistake - there is no shortage of online guitar guitar tabs. Songsterr is a good choice, along with Ultimate Guitar. For the price, it's hard to beat these sites for guitar tabs. That's the good part. The downside to online guitar tab sites is that the reliability is often questionable. I've found tabs at these sites that are close to professional level transcription. Others look like they were done by your cousin Marvin after he had been playing guitar for maybe a month. As long as you're not paying for access, free online acoustic tabs are a great place to start. But there are better choices.
While free online guitar tabs are convenient (and the right price), there's a better choice. If you're really committed to finding the best transcriptions, you should really consider purchasing a professional transcription book. There are at least two reasons why you should consider plunking down the cash for professional transcriptions.
For starters, they're legal. Songwriters and other artists deserve to be compensated for their work, and if you're using an online transcription site, chances are the artists are not being compensated. But perhaps an even greater motivation for most people is that professional transcriptions are just that - professional. That's not to say that a free transcription won't be a good one or that a published transcription will be perfect. But chances are, if you purchase a professional transcription from, say, Hal Leonard that you'll get guitar tabs that are much more accurate. There are also websites like musicnotes.com where you can purchase individual tabs as needed.
If you're a beginner, there are certain artists that have tunes that work really well for those just starting out or who have a limited musical vocabulary. Though they're known for being master songwriters, the Beatles have a large catalog of tunes that are relatively easy to play. Other individual artists or bands that have tunes that work well for beginners include Jimmy Buffet, Bob Dylan, the Eagles, Green Day, Johnny Cash, Bob Marley, Creedence Clearwater Revival, and Tom Petty. And this isn't a criticism, but if you're a country music fan, there are a virtually limitless number of songs that can be played with just 3 or 4 chords (same goes for folk music).