1. Some prepositions, (short words like 'to' 'on' 'about') can change in Welsh. For example:

to Geraint = i Geraint
to him = iddo fe

They change in front of pronouns (words like 'him' 'her' 'them'). You don't need to have all these to use at this level, but here's a list of the three most common (i = to; ar = on; am = about). This is for reference only, but when looking at the endings you see a pattern emerge. Not all prepositions change, e.g. with = gyda (South Wales) / efo (North Wales) doesn't change.

i fi
i ti
iddo fe
iddi hi
i ni
i chi
iddyn nhw

arna i
arnat ti
arno fe
arni hi
arnon ni
arnoch chi
arnyn nhw

amdana i
amdanat ti
amdano fe
amdani hi
amdanon ni
amdanoch chi
amdanyn nhw

2. Adjectives (describing words) coming straight after feminine nouns have a treiglad meddal, e.g. clust dost. There's no easy way of telling if a word is masculine or feminine, without looking in a Welsh dictionary. Here are some examples: merch fach (treiglad from 'bach'); cath fawr (treiglad from 'mawr'). With body parts, if you have two of them, they're generally feminine! e.g. braich (arm), coes (leg), clust (ear). On the other hand trwyn (nose) or pen (head) are masculine.... However, this rule doesn't always work!