The word "substantial" means something between "some" and "a lot". For example, if someone says they lost "a substantial amount of money", that probably means 10% or more of their wealth. Another example:

I earned a substantial amount of money as a teenager through buying and selling comic books at different trade shows and conventions.

Here are some other things that you can have "a substantial amount of":

• spend a substantial amount of time (on something)
• a substantial amount of evidence (that something is true)
• a substantial amount of work (is being done)