With three, four, and five authors, you will cite all of the authors at first mention. Each subsequent mention you will abbreviate to just the first surname followed by et al. For example, the first time Rasmussen, Hopkins, and Fitzpatrick (2004) is used, the source is cited like this:
In research-based development planning, decision-making is based on careful, systematic examination of goals, data, and results (Rasmussen, Hopkins, & Fitzpatrick, 2004).
The second time Rasmussen, Hopkins, and Fitzpatrick (2004) is used, the source is cited like this:
Rasmussen et al. (2004) emphasized the vital role research plays in development planning, saying that thoughtful examination of data and evidence should be present.
With six or more authors, you will only cite the first author followed by et al. the first time and every time. For example, each time Allard, Goldblatt, Kemball, Kendrick, Millen, and Smith (2007) is used, the source is cited like this:
Communities of practice have been used to support the reflective practice of teacher education planning committees (Allard et al., 2007).
Remember that there will not be a comma between the surname and et al., and the period goes only after the al. The English translation of et al. is simply and others.