As you've correctly inferred, it does not matter how you acquired the source code. "Redistribution and use in source and binary forms, with or without modification, are permitted" without regard to how you acquired the code.
There is no need to get permission. Permission has already been granted when the copyright holder chose to license their work under a BSD license. Suppose you did contact the author for permission, and they wrote back, "Sure! I'll go ahead and allow you to use and redistribute that software, with or without modifications, as long as you follow these requirements: 1. Redistributions of source code must retain the above copyright notice.... etc." Such an email would grant you no permission that you don't already possess.
The BSD license allows redistribution but I do not understand what the steps of the redistribution process are.
The requirements are spelled out fairly plainly in the list of conditions, and depend upon the method of redistribution:
- Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
So, you reproduce the license text, copyright notices, and disclaimer, in source code and/or documentation, depending on what you're distributing.
Bear in mind that proprietary or copyleft software may also include BSD license notices if they make use of BSD-licensed code. This means that if you see a BSD license attached to a project, you should carefully note what code it does (or does not) apply to within the project as a whole.