In Oracle Database, how do you extract text in-between characters? (SQL) -

i'm new @ sql , have been trying practice working oracle database.

while working on activity, came across 1 confounds me -- trying extract specific text in-between characters. specific activity cannot seem figure out using these functions is:

for table called users in column called emails, extract email domain (that is, text in-between @ , .), full email addresses:

• mjane@yahoo.com
• jdoe@aol.com
• jbarry@outlook.com

becomes new column called domains values:

• yahoo
• aol
• outlook

so far have been able write code isolates username to:

• mjane
• jdoe
• jbarry

using code:

    `select rtrim(emails,substr(emails,instr(emails,'@')))     studentemails;` 

any extremely appreciated! i've been scratching head hours! thank you!!!

select substr(emails,               instr(emails, '@') + 1,               instr(emails, '.') - instr(emails, '@') - 1) domains users 

caveat:

i assume emails have single dot separating domain name domain type (e.g. com, net). if had email joe@domain.his.us, above query return domain being domain.