The wave mark (tilde) shows e modified by r (/ɜːr/).
Neither short ĕ (bed) nor long ē (be). The letter r curls the vowel into the sound heard in her.
In earn, earth, and learn:
The team ea + r takes the exact same sound as er in her. Silent letter combinations require careful visual memory!
Turns an action verb into the person who performs it:
toil → toiler, call → caller, work → worker, spell → speller. Notice how the base word stays intact!