CreepTD is in fact "the mother of all TD games". So, if you played another tower defense game before, most of the following documentation may sound familar to you to some extend. However, if you never played a tower defense game before, never played the tower wars subgenre that requires you also to send creeps or just played rather simplistic ones, these are the basics:

CreepTD basically is about finding the best compromise between attacking your opponents by sending creeps and defending your lives against incoming creeps by building defense structures (towers). At the beginning you get 200 credits, 20 lives to defend and an income per round of 200 credits. If a creep manages to pass through your game board completely, you will lose a life.

Sending creeps will cost some credits but will increase the income you receive with a new round. One round lasts 15 seconds and when a round is finished your credits will be increased by your current income. With this in mind, the best strategy is based on building as few towers as required and sending as much creeps as possible.

When defending, the rule is to place your towers at strategic locations, e.g. where they are able to hit incoming creeps as often as possible to deal maximum damage. On the other hand you have to select the right tower types for the right purposes, decide whether to build additional towers or to upgrade existing ones and later on adjust your towers' strategy settings to deliver best results.

When attacking you gain an advantage by good timing and selecting the most dangerous creep types depending on your oponents' defense setting. Sometimes it may be the right decision to send a wave of smaller creeps and another time there will be a big creep required to put your opponents under pressure.