How do you use the conditional tense in German?

Konjunktiv II (also known as the subjunctive II) is a verb form which can be used for conditional statements, to express uncertainty, contrary-to-fact statements and polite requests.
To use Konjunktiv II in the present tense, we use [würde + infinitive]. For example, "Ich würde essen" (I would eat).
To use Konjunktiv II in the past tense, we use the subjunctive form of "haben" and "sein" ("hätten" and "wären") and the past participle of the main verb. For example, "Ich habe Deutsch gelernt" (I have learnt German) becomes "Ich hätte Deutsch gelernt" (I would have learnt German).OR "Ich bin nach Amerika gefahren" (I have flown to America) becomes "Ich wäre nach Amerika gefahren" (I would have flown to America.
Remember - we use "sein" (thus "wären") when the verb indicates movement or a change in a state of being.