Bonds are just debts that have been packaged and traded as securities. In a nutshell, they are loans (issued by companies, municipalities and sovereign nations) which can be purchased in consideration of a twice-yearly "coupon" or yield for the duration of the term of the loan plus, naturally, the full repayment of the initial capital outlay.
Bonds are among the weapons of choice for those seeking a steady income from their capital. This is because they are generally less volatile than equities and, because of the way they're structured, they offer a significantly higher degree of protection to the holder should the issuing company go out of business. Stockholders are subordinate to bond holders in the event a company fails; this means that bondholders will always be made whole before stockholders.
Wainright Marks Management typically advises holding bonds issued by national governments and large-cap corporates. Bond prices perform inversely to bond yields so, for example, if the price of a bond rises, the yield (or coupon) payable drops. Conversely, if the price of a bond falls, the yield rises.
Corporate bonds issued by large companies tend to be fairly safe though, in theory, it is the bonds issued by G8 sovereign states that are generally perceived as being the safest available.
Difficult as it may be for some to agree on what represents the best approach to investing, ultimately, the overarching aim is to emerge from a venture with more than that with which one enters having exposed one's capital to as little risk as possible.