Strategies as such (by definition) are plans that affect the overall pattern of playing - how you will win the game. For instance, the plan to wall in first and produce advanced units later or to attack continously from the beginning on are strategies. Now all strategy pages (including mine and Shlonglor's) use that word in a pretty arbitrary, inaccurate and free sense, meaning also tactics.
Tactics are "how to do's", details that affect particular operations, i. e. how to control units, how to attack etc. You need both of them to be successful, and distinguishing both things is not always possible. Most strategy pages contain many tips and tricks that are useful in particular situations, but only few overall strategies. Not the least important reason is that there is no perfect overall strategy that you can follow strictly. Instead, you will have to adapt your strategy to your opponent's actions. It is always important that you do not only produce units, but also plan ahead. Because playing the game is a combination of strategies and tactics, I usually do not always distinguish both terms exactly.