At max. activities and fragments

I am new to android and java programming . I recently came across this

Max. number of events and he says it -

We can have any number of actions, but it is useful to limit a maximum of 25 actions (as Google suggests). We can reduce the number of actions with fragments.

Now the real question I wanted to ask is

• Is every file in the src application considered active ? If this is not so, then which of them can really be called activities ? .java
• Now, since in the above questions the answer involves the use of fragments . But when creating fragments, I still need to create a separate class for each fragment. Now, this is an addition to no. activities?
• If each fragment class is considered an activity, can all its code be encoded in one action?

Another : does too many files affect .javaapplication performance?

Thank you for your help.