Silver trumpets were used to call the people to gather at the tabernacle and to move on, and to mark the various feasts and festivals. They probably looked like the trumpets shown in the Arch of Titus:
There is more detail about these trumpets on The music of the Bible.
The trumpets were also to be used to call the people to war once they had occupied the promised land:
9 When you go into battle in your own land against an enemy who is oppressing you, sound a blast on the trumpets. Then you will be remembered by the Lord your God and rescued from your enemies.
Already, there was a sense that Israel was not to be an infinitely expansionist empire, unlike that of the Romans or the Greeks under Alexander the Great. The new nation would have its boundaries: these were set by God as the land he had promised Abraham.