"Yes, today is my birthday."
Translation:Sí, hoy es mi cumpleaños.
I checked spiceyokooko's link, and while it has SOME good information, it is DEAD wrong on one major point. Go ahead and check it out if you haven't already, but according to my Spanish professor, (a native and fluent Spanish speaker and linguist,) the part about estar (esta in this context, verus es, a conjugation of ser) being used to denote a temporary state is a widely-spread MYTH, and it is, if you'll pardon my being so definitive, it's WRONG.
The example he used was with the word "muerto," an adjective meaning "dead". The grammatically correct and standard way to say, for example, "She is dead." in Spanish is "Ella está muerta." Is being dead a TEMPORARY condition? No, not generally.
The ACTUAL general use difference between ser and estar, (or conjugated, es versus está... and yes, the accent mark matters, without it, if the word requires it, in most cases it's either the wrong word, or it's misspelled,) is one of WHAT something is, versus HOW something is.
For instance: "Ella es profesora." She is a professor. It's not implying her status as a professor is permanent, it's that that is her profession. By contrast, "Ella está muy bien." indicates HOW she is, in this case, very well. Other examples:
Ella es la presidenta. Most presidents are not permanently president. In the specific case of presidents of nations, such as "the president of the United States," the honorific is generally used for life, but not all presidents are of countries. Any meeting of an organization generally has someone who is in-charge, who coordinates events and guides the course of the meeting, such as deciding who gets to speak, (not necessarily for the power trip, just to help keep the speakers from stepping all over each other,) and that would probably NOT be something conveyed for life.
If, say, your grandmother were once to have been president of the PTA, decades ago, do people refer to or address her as "Mrs. Jones," or whatever, or are they obliged to call her "President Jones" for the rest of her life, for all time indeed? No, of course not. That would be silly, unless she were also president of something else at some point, or you were discussing something that happened AT one of the meetings she presided over, such as, "On April 9th, 1952, an exceptional meeting of the Cedar Springs PTA was called to discuss pressing matters of the day. President Jones convened the meeting at 10:05 AM, and began by asking..."
(How funny would it be if she actually were named that, and HAD been president of a PTA, and HAD lived in a place called Cedar Springs... I swear I just made all that up. Be freaky, right?)
Anyway, ser and estar, both translating as "to be" in English, are mostly used as I have indicated, though there are also specific cases and phrases where one or the other is indicated as the appropriate one to choose, and on THOSE points, to the best of my knowledge, the information in the link provided in the previous comment is correct. My only issue with the information found there is the "temporary versus permanent" thing, and if you keep in mind the correct distinction, "what something or someone is versus how he/she/it is," you'll be less confused, I think, in the future.
Just wait until you get into "por versus para," if you haven't gotten there yet. You're going to have ever so much fun with those... and also the various different past-tenses in Spanish. LOTS of fun! :-)
The good news though, is that they actually DO make sense, which is an advantage Spanish has over English. With Spanish, there's actually an organization in charge (the RAE, Real Academia Española, or Spanish Royal Academy,) of what is, OFFICIALLY, "Spanish". We don't have that, at least in America. There are dictionaries, of course, but no one is, generally, legally obliged to follow them, and there are different dictionaries which probably occasionally differ, especially when they're published in markèdly different years. (Yeah, that's right, I just used e-grave... I'm bringing it BACK!) :-D
For example, I'm pretty sure an English dictionary from 100 years ago will have very different things to say on the spelling and use of some words, from what even the same publishing house's same dictionary says about them today.
Not that Spanish is static, though it seems it has changed a lot less over the same time as English seems to have; English, it seems, is a comparatively-rapidly evolving language. My old Spanish professor showed us an example, two bible verses, in Spanish, that were I think something like 500 years apart, or 800... can't recall for certain. They were almost exactly the same, with a few spelling or word-choice changes here and there. He then showed us a sample of English literature contemporary with the archaic Spanish bible verse. As we were, almost all of us in the class, native (if not exclusive) English speakers, we needed no modern text to see how different it was from today's modern English by contrast.
Anyway, hope this helped.
sí: it is written with an accent, and it is pronounced using higher harmonics (in terms of frequencies), and generally with higher intensity, i.e. with stress. It means "yes". si: it is written without an accent, and it is pronounced using lower harmonics (in terms of frequencies), and much lower intensity than any typical word with a stress. It means "if".