Key difference: Both ‘do’ and ‘does’ are conjugations of the verb, ‘to do’. ‘Do’ is used in the first and second person singular and plural and third person plural. ‘Does’ is used in third person singular.

Both ‘do’ and ‘does’ are conjugations of the verb, ‘to do’. ‘To do’ infers that a task or an action is accomplished or needs to be accomplished. The main difference between ‘do’ and ‘does’ is when and in the manner they are used. ‘Do’ is used in the first and second person singular and plural and the third person plural. ‘Does’ is used in the third person singular.

• I do the work daily.
• You do the work daily.
• He does the work daily.
• She does the work daily.
• It does the work daily.
• They do the work daily.

In order to consider when to use ‘do’ or ‘does’, one must understand when to use the verb ‘to do.’ According to Dictionary.com, ‘do’ is commonly used:

• To perform (an act, duty, role, etc.): Do nothing until you hear the bell.
• To execute (a piece or amount of work): to do a hauling job.
• To accomplish; finish; complete: He has already done his homework.
• To put forth; exert: Do your best.
• To be the cause of (good, harm, credit, etc.); bring about; effect: You do credit to your family name.
• To render, give, or pay (homage, justice, etc.): You must do justice to the idea.
• To deal with, fix, clean, arrange, move, etc., (anything) as the case may require: to do the dishes.
• To serve; suffice for: This will do us for the present.
• To make or prepare: I’ll do the salad.
• Etc.

While, ‘does’ is listed as: “a 3^rd person singular present indicative of do.” Essentially, does is used in all the places that ‘do’ is, however in a different verb format. E.g. I do the dishes. She does the dishes. Consider further examples listed below as reference.

Further examples of ‘do’:

• I do not go there often.
• Do you go there often?
• All you ever do is surf the Internet.
• What will you do this afternoon?
• It’s not the best broom, but it will have to do.
• How do you do?
• What does Bob do for a living?
• I'm going to have to do this in the play.
• Do you speak Spanish?
• Do we have time for a quick drink?
• Do they want to come with me?
• I do get up early in the morning.
• We do prepare different kinds of food.

Further examples of ‘does’:

• I play tennis; he does too.
• It does look good, doesn’t it?
• Does he speak Spanish?
• Does John speak French?
• Does it rain a lot in the South?
• Does she like chocolate?
• Does that car cost a lot of money?
• She does the cooking nicely.
• Mary does get up early in the morning.
• Jack does prepare different kinds of food.

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