There are two kinds of dageshim: more here or this video
dagesh lene video
dagesh forte video
|A dagesh lene makes the pronunciation of a BGDKFT letter hard; e.g. a ב is pronounced “v”. A בּ is pronounced “b”.||A dagesh forte doubles the pronunciation of a letter.|
|Only occurs in BGDKFT letters.||Never occurs in a guttural.|
|Never preceded by a full vowel.||Always preceded by a full vowel.|
Note #2: the dagesh in a vav-conversive will never appear in the first letter of the verb root.