(This is a general answer for North American English. There are variations that depend on a person's region, age, and social context.) Brief answer: You are asking about unreleased T and dark L. For unreleased T, the tip of the tongue touches the aveolar ridge behind the upper teeth. For dark L, the tip of the tongue may touch the aveolar ridge, approach the alveolar ridge, or remain near the lower teeth. Longer answer: Except for the glottal stop, the other allophones of /t/ touch the tip of the tongue to the alveolar ridge behind the upper teeth. Stop T (unreleased T) [t̚], aspirated T [tʰ], unaspirated T [t], and flap T [ɾ] all stop the air flow by touching the tip of the tongue to the alveolar ridge and by widening the tongue to press against the teeth. The glottal stop [ʔ] stops the air flow by closing the glottis. The clear L (light L) [l] allophone of /l/ touches the tip of the tongue to the alveolar ridge and air flows over the relaxed sides of the tongue. A clear L occurs before a vowel (examples: late, silly). The dark L [ɫ] allophone of /l/ raises the back of the tongue and air flows over the relaxed sides of the tongue. Depending on the speaker, the tip of the tongue may touch the alveolar ridge, approach the alveolar ridge, or stay near the lower teeth. A dark L occurs after a vowel (examples: wall, milk). ----------------------- Links: Here is a link to an English teacher who understands articulatory phonetics and who demonstrates clearly how to make the sounds of English. https://www.youtube.com/user/rachelsenglish Here is a link for /t/. https://www.youtube.com/watch?v=hGZ9GwrNWmU Here is a link for /l/ https://www.youtube.com/watch?v=FP0jHNoFqWo There are other excellent English teachers who teach slightly different American pronunciations. There are multiple correct pronunciations and the other English teachers are correct also.

For the T in What Happened (if you decide not to make the sound), I don't think you need to push your tongue toward the roof. I see it as a "Glottal T" like the T's in mate/hate/water/slightly. It's pronounced in the throat where the air flow is stopped for an instant. 啊，我才看到，你是香港人啊。那我其实不用打英文吧？油管上，有好多关于Glottal T的教学。 What happened这种，应该是喉咙那里卡一下, 但不需要顶舌头。 What day 这种属于你说的，舌头顶上去，但不release.

They are roughly in the same position. The main difference is that /t/ just taps the roof of the top of the mouth - with only the tip of the tongue. /l/ is produced by putting more of the tongue of the roof of the mouth. It's also voiced (like /d/), whereas /t/ is voiceless. Think of it like this: /t/ is a precision exercise. /l/ is a "lazy" sound where the tongue lingers on the roof of the mouth. Hope it helps!