One of the key features of Gaelic, and which I learnt early on, is that ‘prepositional pronouns’ play a huge part in the language. These include aig (at), ann (on), le (with), and ri (with) to mention but a few of the most widely-used. They’re essential in forming what could be called ‘faux verbs’, such as:
‘S e dotair a th’innte: she is a doctor (lit: there’s a doctor in her)
Tha nighean agam: I have a daughter (lit: there’s a daughter at me)
‘S toil leatha a bhith a’ cluiche ball-coise: She likes to play football (lit: there’s a wish with her to be playing football)
This can take quite a bit of getting your head around, if you’re an English speaker – it requires adopting a completely different mental map of the language. As English speakers, we’re used to using ‘active’ constructions, such as “I like that” and “He has a hamster”, and you literally have to think in a different way to internalise the more ‘passive’ and roundabout Gaelic ways of saying the same things.
What can help is to know which prepositional pronouns are used with which nouns. Our teacher in last week’s summer course kindly gave us a select list of things that are ‘on you’, which is worth remembering. These are some of the things, feelings, and concepts that use ‘air‘:
am pathadh (thirst): tha am pathad orm – tha mi ag iarraidh pinnt (I’m hungry – I want a pint)
an t-acras (hunger): A bheil thu an t-acras ort?
an t-eagal (fear): Tha an t-eagal orra. (She’s afraid.) 
an fhearg (anger): Nach bi an fhearg air? (Won’t he be angry?.)
an cnatan (a cold): Bha an cnatan orm. (I had a cold.)
am fuachd (the cold): Tha am fuachd oirre. (They’re cold.)
an naire (shame): Nach eil sibh fuachd oirbh? (Aren’t youse ashamed?)
an t-ainm (name): Dè an t-ainm a th’ort? (What’s your name?)
càil (thing, mood): Dè tha càil ceàrr air? (What’s wrong with him?) 
am falt (hair): Tha falt bàn oirre. (She has fair hair.)
Of course, there are plenty of other things, some of which are obvious, such as clothes (tha aodach ùr oirnn – we’re wearing new clothes), some not so (a bheil cabhag ort? – are you in a hurry?).
 Use ‘an t-eagal’ (the fear) to say that someone is afraid of something. The single word ‘eagal‘ is used for regret, “I’m afraid that…”, eg Tha eagal orm nach eil Ealasaid an seo (I’m afraid that Elizabeth isn’t here).
 Càil is another word for thing, which could also be ‘rud‘ (pl: rudan). The dictionary has càil as also referring to mood and disposition, but it can be used in non-moody contexts, eg “Bu toil leat càil eile?“.