How is the value of a cryptocurrency determined and where can we see it? suggest some interesting ICO investments that you came across...
The value is determined by some sort of average between the price people are asking if a seller wants to buy and the price the wants to pay for that Bitcoin. Shorter: supply and demand.
But I guess that you know this and want more. You should have searched. For example,
a nice answer comes from 2013.
You can search more with google using something like
value of bitcoin site:bitcointalk.org