What is a third party library license?

I am developing an android app and my app contains many 3rd party library dependencies like gson, okHttp, Picasso, etc.

1) so I need to specify in my application that I have used these libraries in my application?

2) What does it mean Licensed under the Apache License?

3) What if I don't add a dependency and a direct copy of the library files, or include a library module in my application?

4) what's the point

Copyright 2016 .......

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

      

        
        
        
      

    

Do I need to get a license to use this?