Spanish uses the subjunctive for that structure. Subjunctive is a form that English has left aside to favour the past of verbs to express the idea, but you can still see some remnants of it in sentences like "it is time we had a little chat", or "if I were to tell you that...". Some examples: Si tuviera dinero, iría a China = If I had money, I would go to China Most verbs in subjuntive will end in "era", another possible ending is "ese", Si tuviese dinero... They mean exactly the same, the first one (era) is a lot more common. You can get a full list of subjunctive verb formation in several websites and you can always check whatever verb you want on www.verbix.com I hope this helps.

the corret way to say that is : si no hubiera/hubiese llovido correría. this is a conditional phrase. Si hubiese habido mas agua podria nadar = If there was more water I could swim

Correct me if I'm wrong (I'm still learning the nuances of subjunctive), but I think your way of saying it and mine are only slightly different. Yours implies that it rained in the past tense (maybe it's too slippery now to run), but isn't raining now while mine implies that it is raining now. In his particular example, it is currently raining.

I think he wants to say first something in the past and then in present, this is the.correct way for that

Ah, Paula used haber which I considered. Makes sense.