Imagining things: Konjunktiv II
Use hätte and wäre for unreal present situations. With many other verbs, use würde plus an infinitive. A wenn-clause puts its finite verb last; a following main clause begins with its verb.
Understand the idea
Konjunktiv II can describe an imagined present or future, a wish, a polite request or advice. It is not simply a past tense, even when its form resembles Präteritum. Hätte, wäre and common modal forms are especially useful.
Build it step by step
Use the relevant subject ending with hätte, wäre, könnte, müsste or another established form. For many other verbs, würde plus an infinitive is the usual practical choice. A wenn-clause remains verb-final. If it starts the sentence, the following main clause begins with its finite verb.
See it in a sentence
Wenn ich mehr Zeit hätte, würde ich reisen.
Wenn er hier wäre, könnte er helfen.
A useful memory aid
Begin with a present reality, then imagine its opposite. This helps you express a hypothetical meaning instead of choosing a tense only from an English verb form.
A common trap
Do not confuse hatte with hätte or war with wäre. Also avoid würde sein and würde haben as your default when wäre and hätte are the natural forms.