The Spanish ll is not an L. Getting this one letter right fixes tortilla, quesadilla, paella and a lot of names.
LL sounds like the y in "yes"
In almost all of the Spanish-speaking world, ll and y are pronounced the same way: like the y in "yes", sometimes a little stronger, closer to the j in "jeans". Linguists call this yeísmo.
Listen: calle pollo llamar llave lluvia.
So the food words English speakers say with an L are really y words: tortilla is tohr-TEE-yah, quesadilla is keh-sah-DEE-yah, and paella is pah-EH-yah. Same for places and names: Sevilla, Mallorca, Puerto Vallarta, Guillermo.
Y as a consonant and as a vowel
Before a vowel, y is the same consonant sound: yo, mayo, playa.
On its own or at the end of a word, y is a vowel that sounds like ee: the word y ("and"), hoy, muy, Uruguay.
Argentina and Uruguay: "sh"
Around Buenos Aires and Montevideo, ll and y sound like "sh" (or the "s" in "measure"). "Yo me llamo" sounds roughly like "sho meh SHAH-moh", and calle like "KAH-sheh". It's the most recognizable feature of Rioplatense Spanish. If you're learning for Mexico, the US or Spain, use the y sound.
An older "ly" sound
A few regions, including parts of northern Spain, the Andes and Paraguay, still keep ll as a separate sound, similar to the "lli" in "million". You don't need to learn it, but you may hear it from older speakers there.