We say suprabhaatam (सुप्रभातम्) in Sanskrit in order to say 'good morning'. Namaskaaraha (नमस्कारः) and namaste (नमस्ते) are very popular words in Sanskrit. They are very common spoken greetings. They broadly mean, 'the divinity in me bow to the divinity in you'. Namaste is often used to greet while people meet or depart, during any time of the day.
Shubhamadhyahnam (शुभमध्याह्नम्) can be used for 'good afternoon'. And 'good evening' is shubhasaayam (शुभसायम्). We say shubharaatrhi (शुभरात्रिः) in Sanskrit, to say 'good night'.
Dhanyavaadaha (धन्यवादः) means 'thank you'. dhanyavaadaha (धन्यवादः) is quite and expensively used word in Sanskrit. susvaagatam (सुस्वागतम्) means 'welcome'. Kshamyataam (क्षम्यताम्) in Sanskrit, to say 'Excuse me'. Chintaamastu (चिन्तामास्तु) means 'No worries'. The word krapayaa (कृपया) means 'please'. For example krapayaa atra aagachchatu (कृपया अत्र आगच्छतुतु) would mean 'please come here'.
bhoho (भोः) is an 'indeclinable', that is often used to greet a person. Kim bhoho (किं भोः) is very often used, which broadly means 'Hey, what's up'. The indeclinable bhoho (भोः) is also used to 'address a person'. bhoho atra aagachchatu (भोः अत्र आगच्छतु) would mean 'Hello, come here'. Shreeman (श्रीमन्) and maanye (मन्ये)or aarye (आर्ये)are used to say 'sir' and 'madam'. For example shreeman krapayaa atra aagachchatu (श्रीमन् कृपया अत्र आगच्छतु) would mean 'Sir, please come here'. Maanye/aarye krapayaa atra aagachchatu (मान्ये/आर्ये कृपया अत्र आगच्छतु) would mean 'Madam, please come here'.
Punaha milaamaha (पुनः मिलामः) means 'see you again'. Astu (अस्तु) means 'Okay'. For example when I say punaha milaamaha (पुनः मिलामः) you would say astu punaha milaamaha (अस्तु पुनः मिलामः).