If you look at the standard structure of such a flow it has 3 sections: WHEN (Als), AND (En) and THEN (Dan).
The AND section/group contains flowcards that check whether a condition applies, for example the temperature is higher than 20 degrees.
Normally all conditions that you include in the AND section need to apply in order for the flow to continue. You can however also contain an OR condition as explained in the knowledge article. In such a case either of the conditions need to apply, instead of all.
Below an example with two conditions. In the first screenshot both conditions (luminance and temperature) need to apply (AND). The second screenshot either of the two need to be true (OR / Of).
Or begin in the “Creating your first Flow” article on the page linked to, there it is shown in the video and described in the text.
As mentioned, this is for the standard flows, if advanced flows are available to you I think it’s more fun using that instead.
Either way, understanding the basic concept of “When" is usually the first hurdle to anyone starting out with Homey.