Traditional Distribution

Traditionally, films are distributed by a professional distributor, who uses their expertise to optimally market and distribute a film.
A producer rep usually acts as a middle man between the film maker and the distribution companies. Typically they are payed by the film maker a percentage of the movie sales made after distribution. Their job is to advertise and represent a film maker's movie so that distributors will sell it to theaters, DVDs, and streaming services. But this is not the case for all movies; Usually, a producer rep will sell movies in bulk instead of individually, so film makers can be disappointed with their sales.  However, as indie films become more popular, the need for this middle man in this process is slowly being fazed out, so film makers might eventually work directly with distributors in the future.
Once the movie gets to a distributor, the movie is usually showed in movie theaters around the country for 90 days, then it gets put onto DVD and other VODs after the first 3 months. However, this 90 day time window has been shrinking, and some new movies have requested to go to VOD sooner than 3 months. Occasionally, a movie will show in theaters and on VOD simultaneously, or eliminate a theatrical release altogether.
To summarize, traditional distribution of a film consists of giving the movie to a producer rep who advertises it to distributors who hopefully release it in theaters and VOD.