Learn English – the difference between “do” and “make”

You correctly suspect that “make” is associated with creation. Conversely, “do” will be associated with completion, especially completion of actions and work. For a more in-depth look at the differences, let's start with a readily available resource.

From the Woodward English site, the top-ranked result in a search for “do vs make”:

When do you use DO?

DO is used as follows:

1. DO is used when talking about work, jobs or tasks. Note, they do not produce any physical object.

• Have you done your homework?
• I have guests visiting tonight so I should start doing the housework now.
• I wouldn't like to do that job.

2. DO is used when we refer to activities in general without being specific. In these cases, we normally use words like thing, something, nothing, anything, everything etc.

• Hurry up! I've got things to do!
• Don't just stand there – do something!
• Is there anything I can do to help you?

3. We sometimes use DO to replace a verb when the meaning is clear or obvious. This is more common in informal spoken English:

• Do I need to do my hair? (do = brush or comb)
• Have you done the dishes yet? (done = washed)
• I'll do the kitchen if you do the lawns (do = clean, do = mow)

When do you use MAKE?

[1.] Make is for producing, constructing, creating or building something new.

[2.] It is also used to indicate the origin of a product or the materials that are used to make something.

• His wedding ring is made of gold.
• The house was made of adobe.
• Wine is made from grapes.
• The watches were made in Switzerland

[3.] We also use Make for producing an action or reaction:

• Onions make your eyes water.
• You make me happy.
• It’s not my fault. My brother made me do it!

[4. We use make with] certain nouns about plans and decisions:

• make arrangements
• make a choice

[5.] We use Make with nouns about speaking and certain sounds:

• make a comment
• make a noise
• make a speech

[6.] We use Make with Food, Drink and Meals:

• make a cake
• make a cup of tea
• make dinner

Now that we're on the same page, let's apply this knowledge to your examples:

I made supper.

This fits “make” sense 6 above, which is really just a special case of sense 1. The thing being constructed (so to speak, out of various ingredients) is a meal.

I'm doing my homework now.

This is essentially the first example in sense 1 of “do” above. Homework generally consists of one or more tasks, and is done like a job.

He made it easier.

This one's a little trickier, but it falls under sense 3 of “make” above, which is all about effecting a change in something (or someone) else. In cases like these, the phrase can easily be rewritten without “make” by using some form of “cause (it) to (be)”. For this particular example, you are essentially saying
“He [caused] it [to be] easier”, but that isn't how anyone is likely to say it in everyday parlance.

Note: I've extracted the key distinctions in my block quotes, but be sure to click the link above if you are at all interested in more examples, a helpful chart, and/or a practice test.

Also, please comment if there is some particular aspect of this distinction that is still bothering you.