They are equivalent to English forms such as If I were rich or If I loved him, (but also It would be great) and exist for every verb in the present and imperfect tense.
הן מקבילות לצורות באנגלית כגון If I were rich או If I loved him (אבל גם It would be great), והן קיימות בשביל כל פועל בנטיית ההווה והעבר.