1. To go to school - to get education.
e.g. Sheila is going to school. (It means Sheila is studying there).
To go to the school - to go for other purpose
e.g. Sheila's father is going to the school. (It means Sheila's father is visiting school for some purpose, may be inquiring about his daughter's progress.)
2. To go to play - to take part in games
To go to the play - to go to a theatre.
3. A black and white dog - One dog which is partly black and partly white.
A black and a white dog - two different dogs - one black in colour while the other is white in colour.
4. Tell me briefly - Tell me in a short time.
Tell me shortly - Tell me in short.
5. The eldest son - The first born son.
The oldest son - The oldest of all the living sons.
6. Who is your father? - Asking name of your father.
What's your father? - Asking occupation of your father.
Which one is your father? - Asking to identify your father among a group of persons.
7. I differ from you - In appearance
I differ with you - In views only
8. Work hard - to put in labour
e.g. Ram worked hard that's why he scored good marks.
Work hardly - scarcely
e.g. Shyam worked hardly, that's why he scored poor marks.