Therein lies a clue to the conga's role. At its most fundamental it provides the backbone of the rhythm section, in a way that tastefully underpins the montuno and bassline.
The head-sizes vary from 9 3/4" (24.7cm) to 14" (35.5cm) in diameter. The smaller drum is called the quinto and is used for soloing. The middle sized is called the conga and is probably the most versatile in terms of tuning. The largest one called the tumba provides the low frequency tones that are commonly used as groove accents. Congas are generally sold in quinto-conga pairs, which are ideal starting points.
The shells themselves are either fibreglass or wood. Fibreglass has a little more flex so they are kinder to the hands, have more sonic projection, and are lighter to carry - all boons if you gig regularly. Congas made with wood produce a warmer tone.
There are two general types of rims: traditional and comfort. Misplaced strokes on a traditional rim are a painful experience, so I would recommend the comfort rims to beginners unless you're a glutton for punishment. There should always be hardware mounted on the shells to allow tuning of the drumheads.
Skins can be natural hide or artificial. Natural skins have a great sound and touch but are vulnerable to changing conditions: humidity, perspiration, and heat from stage lighting or playing; and need to be re-tuned constantly. Get the best quality skins you can afford so that you can develop your touch - cheaper skins are thicker and require more impact force to activate a tone. One option is to go for a budget conga and fit a good artificial skin.
Artificial skins such as the Evans Tri-Center and Remo Fiberskyn have fewer vagaries, and are capable of producing good tones, but some musicians remain unconvinced as to the "authenticity" of sound. Like naturals, they can take a little while to bed down, and the latter are less prone to rupture from accidental impact while under tension.
Brands to investigate as a starting point are Latin Percussion, Meinl, and Toca.
What to play
Also work on a strong metronomic time-keeping march of the non-dominant hand, which will both stabilise your patterns and provide a reference timeframe to which you can calibrate the strokes of your dominant hand.
Suggested patterns and variations to start with are (in order):
Latin-American Percussion: Rhythms And Rhythm Instruments From Cuba And Brazil by Birger Sulsbrück. (External link)
Salsa Guidebook For Piano & Ensemble by Rebeca Mauleón. (External link)
Getting Started On Congas Series by Bobby Sanabria. A three videotape set from the Grammy® award-winning percussionist. Great for laying down the fundamentals of conga playing. (External link to second tape in the series)
Conga Drumming: A Beginner's Guide To Playing With Time by Alan Dworsky & Betsy Sansby. The first of a series of engaging books developing percussion as an skill. (External link)
The Tomás Cruz Conga Method Series by Tomás Cruz. The most comprehensive programme I have yet come across. Making the leap from the fundamentals to what is actually being played by timba congueros has never been so completely described. (External link)
Salsa: Ear Training by Loo Yeo. (Link to section)
Lessons page of Alex Pertout's website by Alex Pertout. (External link)
& Merengue Society