Much like woodwind instruments, the use of brass instruments in the orchestra depends on the period of music.
In the Baroque period the high trumpet was used in a lot of orchestral music.
In the Classical period brass instruments (French horn, trumpets) mainly accompanied the strings. When the valved trumpet was developed by Anton Weidinger, Haydn wrote a trumpet concerto to explore the full range of this trumpet. Mozart also wrote five horn concertos.
In the Romantic period and beyond, brass instruments gained more independence in orchestral music. Brass instruments were often used by composers for their distinctive sonorities.
As well as general instrumental techniques, brass writing often includes the use of mutes. A mute in a brass instrument makes the music quieter and changes the sonority of the instrument. You can hear this in the head section of Miles Davis’ All Blues:
The ‘wah wah’ effect of a brass instrument is created by the performer by moving a hand in and out of the bell of the instrument (usually a trumpet).