An instance can be found here.

What it means:

1. You can modify the code and you don't have to tell anyone that you did it nor do you have to give those changes to any authority, Apache or otherwise.
2. If you publish anything using the code, you must offer a copy of (this) license.
3. You must say in the code that you have changed something.
4. You can add your own notice alongside the Apache one, but you must be careful not to claim that Apache is somehow an author of your product (derivative work).
5. Neither Apache nor anyone else, but yourself can be held responsible for the original and derivative code or its impacts of use.
6. How to apply this practically. You attach a boilerplate notice thus:

Copyright [yyyy] [name of copyright holder]

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.