Its purpose is to improve the child's handwriting, expose them to noble thoughts, good sentence structure, rich vocabulary and introduce basic punctuation and capitalization rules. Even grammar is incidentally taught but this is just an added benefit and not the purpose for copywork.
Many wonderful essays have been written on copywork and how to apply it so I do not wish to be repetitive. You can get some help here, for starters. I am just going to list a few things that we do in our home.
Copywork is scheduled three to four days a week . ( On the fifth day, the children decorate their pages with pretty borders and/or pictures cut from magazines, etc...that illus. the passage if they wish.)
Usually, a different kind of passage is done for each day of the week so that the child is exposed to a variety of writing. It also keeps it fun. e.g. Monday-Bible, Tuesday- Literature, Wednesday- Poetry, Thursday-Quotes.
I write a perfect model on the dry erase board for the youngest children. The older children copy from their books. (First year students who are just learning to form their letters copy from a model that is on their page, not just on the dry erase board)
I do not use a handwriting program for printing letters because they require the child to write too much. Plus, it is so easy for myself to just print the letter on the child's page. The parent SHOULD have a handwriting chart so that she doesn't model the letter incorrectly. (don't trust your memory.) If you are uncomfortable teaching cursive to the older children, then a workbook may be in order. I've never used one. I just looked at a cursive chart and modeled it. (edited: here's a helpful handwriting worksheet site.)
They copy from rich literature passages. They never copy from twaddle or their own writing so that they are exposed to well-crafted sentences with correct grammar, punctuation and spelling.
They never copy a passage twice and we use a different passage for dictation.
I keep two jars filled with little pieces of paper. One jar is filled with famous quotes suitable for younger children. The other jar has quotes for older children. They pick out two and choose from one of them. If they don't finish a passage, they just work on it the following week, not the next day.
The younger children often help in deciding what book or passage the selection will come from, but I make the final decision. I caution against using copywork as a means of preaching morals to our children. If a child is only allowed to use this time to copy scripture, rules of conduct or little ditties that moralize, then I feel there is a danger of resentment forming within their heart. It is a difficult task to begin with since their hands are learning fine motor control, so let us make it as pleasant as possible by keeping a variety of sources delightful to the child. I like to pick a couple passages from their own schoolbooks and let the children choose from them.
First year students use this time to learn how to form their letters on large triple lined paper. They do not copy passages yet. Later in the year, they begin to copy simple words and phrases. (Label nature journal entries, items in the schoolroom, their name, etc...)
No sloppy letters allowed. Not one undotted 'i' is allowed; not one punctuation mark omitted. Quality over quantity is the idea. Go here for my post on perfect execution.
I do not introduce written conversation within quotation marks to first and second year students. This can be confusing for them while they are still trying to learn to write a basic sentence.
I use a timer and hover so that no talking or daydreaming occurs. I watch to make sure they are starting at the top of the line rather than the bottom. The first year students draw the letter in the air first, with me so they understand the general strokes and direction.
The youngest work just 10 minutes. Older children work 15 to 20 minutes. If they dilly dally, that wasted time is added to the timer. My teen no longer needs a time frame. She records the passages in her commonplace book.
The youngest make corrections immediately, but the older children turn theirs in and I check it later. I just put a tiny red dot under ill formed letters so that I don't mess up their page and we discuss, then they correct.
I tell them at the beginning of the year that they are making a beautiful book of noble thoughts. Each page is treated carefully and compiled into a decorated duotang type folder until they begin a commonplace book in a journal. They make a new book each year.
That's all I can think of, right now. If you still have any questions, leave a comment and I'll try to address it; but first, please check the link I gave. Most questions will be answered there.