What is a dual? A dual verb ending refers to exactly two people, and it allows you to say sentences like "You both liked the lembas" or "He and she are both growing roses in their gardens". English has very few words left that have a dual distinction (the most obvious is the word 'both'), but it does exist in other languages like Arabic. The 'we and you' ending in Sindarin is what's known as a trial ending (referring to three items).

These endings can only be used on the Present Tense
Don't forget to apply I-affection to I-stem verbs

Dual endings (I-stem)

We (not you)	-immid
We (and you)	-ingid
You both (formal)	-idhid
You both (informal)	-ich
He/she/it both	-ist

Dual endings (A-stem)

We (not you)	-ammid
We (and you)	-angid
You both (formal)	-adhid
You both (informal)	-ach
He/she/it both	-ast

Examples

Lastammid na Elrond = We are both (but not you) listening to Elrond
Os-rigimmid loth in yrn  = We are both (but not you) twining flowers around the trees
Sabammid an valt = We are both (with you) digging for gold (We three are digging for gold)
Ledhingid na Vree = We are both (with you) travelling to Bree (We three are travelling to Bree)
Taethadhid i chebaid lîn = You are both fastening your shoes (formal)
Ceridhid i annabon = You both see the elephant (formal)
Nauthach = You are both thinking (informal)
Gledhich o nad = You are both laughing about something (informal)
Aderthast adh i vuindor dîn = He and she are both reuniting with their dear brother
Gerist i orn han! = He and him are both holding that tree!