The three constructions “als ob,” “als wenn,” and “als” (as if/as though) function as subordinating conjunctions that are most often used with the general subjunctive (der Konjunktiv II). Typically, this means that the conjugated verb in the clause in which these conjunctions appear should be located at the end; however, in the case of “als,” the verb will come immediately after the conjunction. The most commonly used conjunction is “als ob,” though all three are seen commonly in the subjunctive.

Examples: 
Daniel hat uns befohlen, als ob er unser Chef wäre.
Daniel has ordered us around, as if he was our boss. 

Julia spricht von der Zukunft, als wenn sie schon wüsste, was passieren wird.
Julia talks about the future, as if she already knew what will happen. 

Vera gibt Geld aus, als wäre sie reich.
Vera spends money, as if she was rich. 

“Als ob/wenn” and “als” clauses are typically used to form unreal comparisons “irreale Vergleiche”. Clauses that use “als ob/als wenn” and “als” typically answer the question “Wie?” (How?)

Examples:
Wie sieht er heute aus? 
Er sieht aus, als ob er die ganze Nacht nicht geschlafen hätte. 
How does he look today?
He looks, as if he hasn’t slept all night. 

We could also answer the above question with “als”, but then we need to remember that the verb no longer moves to the end of the sentence:

Er sieht so aus, als hätte er die ganze Nacht nicht geschlafen.