In addition to the Coptic letters, the Coptic Language also make use of a dot-like phonatic symbol.  The GINKIM was not part of the original language, but was added to help readers pronounce the words.  There are various forms
for the GINKIM (`    ~    =    ) and though some argue that the shape affects the opening of the mouth, it's generally accepted that they're all pronounced alike.

The Rule:

I. When it comes over a vowel letter, it splits the word, because the letter must be pronounced by itself.

A. First, we need to know the Coptic vowel letters:

The way I learned them is to first write the English vowel letters and then match their Coptic counterparts:
(English)    A    E       I    O       U
(Coptic)    a    e    3    i    o    v    w
Note: Y is considered a vowel because when it follows an O, it is pronounced an O; some authers consider OY rather than just Y as a vowel

B. Examples:
 

A`aron	is pron. A_a_roon      means   Aaron
Mari`a	Mari_a                Mary
`Ebol	E_VOL                 Of
Pek`3poc	PEK_EE_POC            Your Garden

 
II. When GINKIM comes over a consonant letter, an e sound proceeds the  letter.

A. For Example:
`k = ek         `m = em         `n = en         `d = ed

B. Real Examples:
 

` K`cmarwovt	is pron.   EK-ES-MARO-OOT   means You are Blessed
` Nnovb	EN-NOUB                  The Gold
` MMariam	EM-MARIAM               Of Mary

III. Try reading these words:
 

Word	Meaning
A4`i	(He) Came
)e`otkoc	Mother of God
`Eron	(unto) us
All3lovia	Alleluia
Pi`ehoov	The day
Ei`e`i	I must come
`Ajioc	Holy (Greek)
`Xovab	Holy (Coptic)
%`triac	The Trinity
`Nte	Of
`Precbvteroc	Presbyters (priests)
`Fran	The Name
@ep`hmot	Thank (you)
`Apctoloc	Apostle
`Al30wc	Truely
Pi`wov	The Glory
`Am3n	Amen