"Create an Account" or "Create Account"
Solution 1:
In titles, labels, and captions like that, we routinely omit articles and other words not essential to the meaning in order to keep it short. So if you were writing a sentence, you would write, "Create an account". But for a label you would normally drop the article.
In titles we usually capitalize the first letter of each word, except for articles, conjunctions, and prepositions (unless the article, etc, is the first word of the title, in which case it is capitalized). For example, "The Care and Feeding of Rabbits" or "History of the English People". (Sometimes these words are capitalized when they are considered important. Like, "Strange But True" -- you don't want the reader to skim over the "but" or he'll completely miss the point.)
Thus, the conventional thing to use would be, "Create Account". No article, both words capitalized.
If you do decide to include the article, it should be "Create an Account". Article not capitalized.
Solution 2:
Use:
create an account
create account
create new account
create a new account
"Create the account" is grammatically correct, but is rarely used.
Capitalization is up to you. You may leave capitalization altogether, if you want. But remember one thing: you can either capitalize just the first word or capitalize all (you may or may not capitalize the articles - a, an).
Solution 3:
Conventionally, articles are omitted in labels. Apple uses the following style (assuming it's a computer form):
Create Account
Delete Account
Solution 4:
I think
create an account
is better, in fact the best among your options, assuming that we are referring to a single account.
And
create the account
should only be used, when you are referring to an account you have mentioned earlier.
As far as capitalization is concerned, I agree with our friend rudra.