The symphony is a musical form of enormous diversity. Composers started writing them frequently around the middle of the 18th century, and have continued to produce them to the present day. The term comes from the Greek meaning "To sound together", and long ago, what we now call tge overtures to operas were "Sinfonias ". A typical opera overture of nearly 300 years ago would start with an orchestral introduction, typicall in three parts, fast, slow and fast. Then composewrs started writing music like this as independent music to be heard at concerts. Thus the symphony as we know it was born. To this day, overtures to a variety of operas, such as those of Wagner and Verdi (19th century) are often heard as openers to concerts.
The first great symphonies were written by Haydn and Mozart, circa the last half of the 18th century. Haydn wrote 104 of them in his long career !
There are 41 numbered ones by Mozart, and several ones which are not numbered. Beethoven revolutionized the symphony, writing ones of unprecendented length and complexity, culminating with the monumental 9th, with its famous "Ode to Joy " with chorus and four vocal soloists.
A symphony can last under fifteen minutes, and the great Austrian composer Gustav Mahler who wrote nine, with an unfinished tenth, wrote symphonies that last from about an hour to 90 minutes, also using voices in four of them. Try the famous "Unfin ished "symphony, no 8, by Franz Scubert, (1797- 1828 ). Schubert completed only two of the usual four movememts. No one knows why, but there has been a great deal of speculation. We will probably never know. But it's a great piece. Then try his 9th and last symphony, known as the"Great", to distinguish it from an earlier symphony he wrote in the same key which is much shorter.
Then you might try two of the five symphonies by Felix Mendelssohn (1809- 1847 ). The third is called the "Scottish", as it is an evocation of the composer's visit to that country, and is full of local color. The fourth, known as the "Italian", is also the result a a trip to that country, and ends with a lively Italian dance called the "Saltarello". Robert Scumann (1810- 1856 ), wrote four beautiful ones, the first called the "Spring" symphony, an evocation of that pleasant season, and the third called the Rhenish", based upon Schumann's stay in the German Rhineland.
Johannes Brahms, (1833- 1897 ), wrote four gorgeous symph onies that are staples of the repertoire. Peter Ilyich Tchaikovsky of Russia wrote six. Only the last three are played often for some reason, but they are all worth hearing. They are very Russian, chock full of great melodies and very intense. The Frenchman Camille Saint- Saens (1835 - 1921 ), wrote five, but only the numbered third is played with any frequency. It is a spectacular work called the"Organ " symphony, as it features a prominent part for that instrument, which is very unusual.
The Czech Antonin Dvorak (1841- 1904 ), wrote nine, but only the last three are performed very often, although you can occaisionally hear the earlier ones at a concert. All are delightful and very Czech, with marvelous tunes. The most famous is the 9th, called"From the New World", as it was written during the three years the composer spent in America. Dvorak became very interested in the music of African-Americans, including spirituals, and the music of the native Americans. Dvorak did not quote any American folk tunes; he wrote in the spirit of American music.
This is only a beginning; there are also many great 20th century symphonies by composers such as Shostakovich and Prokofiev of Russia, Finland's Jean Sibelius, and many others. There are countless performances on Cd; check the internet sites I mentioned before for recommendations.