What does grants to the publisher and its licensees "for the full term of the copyright available.... the following Primary and Secondary rights" mean?
It means you're granting the rights specified in the contract for the full term of copyright, which is the life of the author plus 70 years. Primary rights usually means book rights--printing and distributing the book in various parts of the world. Secondary rights, also known as subsidiary rights, might include book club, dramatic, audio, film, serial, translation, and others.
Before you get alarmed about "life plus 70", this is standard publishing contract language (though not optimal for an electronic or digital publisher--more on that below). However, it MUST be balanced by a clear and unambiguous termination/out of print clause, which specifies exactly how and under what circumstances a book will be declared out of print, and what steps you can then take to get the rights returned to you. Many small POD-based publishers, which are often run by people without publishing experience, have poor or unclear termination clauses, or may even omit a termination clause entirely.
As I noted above, "life plus 70" isn't ideal for a digital or electronic publisher. This is true for a variety of reasons--their books typically sell in small quantities and for a short period of time, they often go bust after only a few years in business, and their lack of business expertise often makes for all kinds of problems, from nonpayment of royalties to nonproduction of books. Also, things in the digital universe change fast, and if there's a better option you want to be able to jump on it. All of this means that you don't want to be tied to an e- or digital publisher for too long. Either a time-limited contract (1-3 years) or a contract that allows you to terminate at will with adequate notice is far
preferable to "life plus 70".
Another issue: smaller publishers often aren't capable of marketing secondary or subsidary rights (many of them are aren't capable of marketing their books, but that's a whole 'nother can of worms). A publisher shouldn't demand rights it isn't able to sell. Yet many small publishers want a whole smorgasbord of subrights, and often aren't willing to negotiate this.