Deuteronomy 1:22 (ESV)

22 Then all of you came near me and said, ‘Let us send men before us, that they may explore the land for us and bring us word again of the way by which we must go up and the cities into which we shall come.’

In spite of Moses' word not to be afraid, the people were afraid and so planned to send spies ahead instead of believing as Moses had called them to do. They wanted to send spies who were to explore the land and then advise on the best line of attack and also report on the size of the cities.