There are several usage of the particle ‘leoi’
1. เลย [leoi] is a particle used when you tell someone to do something immediately. In English it would be ‘go ahead’
กินเลย [gin leoi] in English it would be ‘please go ahead and eat now’
ไปเลย [bpai leoi] in English it would be ‘go ahead’
ทำเลย [tam leoi] in English it would be ”go ahead and do it now’
2. เลย [leoi] is used for emphasis at the end of a statement, similar to the English words – so much!, extremely!, completely! indeed!
ผมหิวมากเลย [pŏm hĭu mâak leoi] means I’m very hungry.
หนังไทยสนุกมากเลย [năng tai sà-nùk mâak leoi] in English it would be Thai movies are really fun.
3. จัง [jang] , จังเลย [jang leoi] is also used for emphasis at the end of a statement. It is informal.
ภาษาไทยง่ายจังเลย [paa-săa tai ngâai jang leoi] = Thai language is very easy.
อาหารไทยอร่อยจังเลย [aa-hăan tai aròi jang loei] = Thai food is very tasty.
ลูกแมวน่ารักจังเลย [lûuk-maew nâa-rák jang leoi] in English it would be ‘What a cute kitty!
NOTE: There is a difference between มาก [maak] and จังเลย [jang leoi], when you use them to describe some quality or feeling. They are both quantifiers, maak denotes “very” when go with an adjective, while it means much/many when used with a verb or noun. On the other hand, จังเลย [jang leoi] carries the speaker’s personal feeling with it and therefore it sounds much sweeter and more personal.
Compare: คุณสวยมาก [kun sŭai mâak] = you are beautiful (you just give a description) and
คุณสวยจังเลย [kun sŭai jang leoi] = My feeling or my heart tells me that you are so beautiful
4. ไม่…เลย [mâi…leoi] in English would be not…at all
เขาไม่กินอะไรเลย [káo mâi gin à-rai leoi] = she is not eating anything at all.
ที่นี่ไม่มีร้านอาหารญี่ปุ่นเลย [tîi-nîi mâi mee ráan aa-hăan yîi-bpùn leoi] = there is no Japanese restaurant here.
FUN FACT: เลย [Leoi] is also the name of a province in North eastern Thailand. It is surrounded by mountain ranges whose summits are covered by fog and are abundant with various kinds of flora. The best known mountains in the province are Phu Kradueng, Phu Luang and Phu Ruea.I went up to Phu Kradueng few years ago. See photos here
I hope you found this lesson useful:)