Why every time I search for albums on Funk or Soul, for example in music apple, most of the albums that are supposed to be funk as labeled as soul/R&B?? What makes these three genres different? Why do they try to put them all together?
"R&B" ("Rhythm and Blues") was a term coined by then-journalist Jerry Wexler of the industry-trade publication Billboard Magazine in 1948. The term "R&B" was first used by the radio and recording industry in the USA to describe all recorded music marketed to African-Americans. The term that "R&B" replaced was "Race Records" meaning records marketed to the minority African-American race. "R&B" was not originally a term that any musicians or bands used to describe themselves or their music. So when the term was created it did not describe any genre per se. It described nothing other than a specific marketing plan used by record companies and radio stations in that era.
Any artist or band in that era wouldn't spend any time thinking about whether they were "soul" or "R&B"; they would just make music and try to get it sold and earn income through the record business and radio business.
"Funk" is a little different, because to the best of my knowledge there was never an actual recognized commercial radio format in the USA called "Funk". Funk is a distinctive style that originated in the 1970s, usually characterized as African-American popular music with an emphasis on a certain distinctive heavy beat. There were bands that identified themselves as funk bands back in the day.
It would be correct to say that "R&B" encompasses all popular music made by African-American artists and marketed to the African-American public. "Soul" and "Funk" are each subsets of the larger category of "R&B".
For full background information and references that demonstrate the points I've just made, please read my previous answer to this question:
Wheat's excellent answer covers the context, but read on for an (admittedly subjective) evaluation of the musical differences:
R&B has encompassed many different styles over its lifetime, and continues to be a term in current usage today. In general, it has typically meant the style of vocals-oriented pop music most popular among "urban" (black) listeners at any given time --music that may have a large crossover audience, but whose core audience and tastemakers are black. It has encompassed figures as distinct as the Temptations in the 60's, Bobby Brown in the 90's and Frank Ocean today.
Soul music is essentially a secularized form of black gospel music, with heartfelt, passionate vocals and a smooth "soulful" sound. Topics are typically romance, romance-gone-wrong and occasionally social issues. Major exponents include Ray Charles, Isaac Hayes, Aretha Franklin and Marvin Gaye.
Funk is a much rougher style characterized by rhythmically complex, syncopated instrumental lines used for percussive effect (as in the scene in the James Brown biopic where every instrument is described as "a drum"). Crunchy synthesizers, distorted guitars (played on the 16th note) and brassy horn sections are all typical of funk. The word "funk" is often used to describe a strong, organic body odor, and the music has some of the same raw, in-your-face connotations. James Brown, Earth Wind and Fire, Sly and the Family Stone, and Parliament Funkadelic are all big names in the funk genre (recently revived in Mark Ronson and Bruno Mars' hit "Uptown Funk"). Funk and Soul are both subgenres of R&B and one song can fit all three categories at once (i.e. James Brown's "Man's World"). Since both sub-genres were popular with similar audiences and (arguably) reached a peak in the 70's, there's plenty of overlap.