Galaxyrocker is correct.
If you aren't 100% sure what the SUBJECT form is, look for the person or thing that performs the action: WHO (or what) drinks, eats, reads, etc?. Those will be sé/sí/siad.
Once you have that, look for the person or thing that receives the action: The child eats WHAT? I see WHOM? That's your OBJECT.
Remember that sentence from a lesson or two ago, "Itheann an leon na páistí"? (How could you forget?) The verb is itheann. WHO is eating? The lion, so he'd be the subject: sé. The lion eats WHOM/WHAT? The children. They'd be the object: iad.
About the copula--you know how in English we're not supposed to say things like "It's me" or "That's him"? Well, those constructions are correct in Irish! That's he/him!-->Seo é. (Literally "that him"--you can leave the verb out in this case.) He's a doctor--Is dochtúir é I'm sure there will be a lengthy lesson on this tricky verb later!
I would strongly suggest that you get a good Irish book (Gaeilge gan Stró or Now You're Talking, for example) that comes with CDs, if you cannot find an Irish class in your area.
You will do that in the best, most accurate manner, not missing any sounds, with (Best) an extended stay in the Gaeltacht (Next) a live class with a native or near-native speaker as a teacher (Next) a good textbook with an audio component (Worst) Duolingo, especially if you can't read IPA (most people can't)
If you're serious about learning Irish, you need to get a textbook. If you're not serious, it doesn't matter.
This video is pretty good: https://www.youtube.com/watch?v=oIokUII7LX0
I've spoken Irish and live in Ireland for a few years now but that pronunciation is brutal. If you can can you revise some of your audio please. For example "leabhair" is pronounced like "low-ed" rather than "low-er" which is not very understandable from a listener's perspective
This comment is so wrong it's scary. The audio on this course uses recordings of a native Irish speaker from Connacht.
English speakers who can't really hear the difference between a broad r and a slender r sometimes claim that the slender r is more of a "d" sound. It's not, and the speaker in this exercise properly pronounces the slender r sound in leabhair (you can compare it to the Munster example at teanglann.ie - the Connacht and Ulster examples use dialect pronunciations).
You can also hear other examples of words ending in ir at fuaimeanna.ie - it is not a "d" sound!