An Inventory count shows $210 of cleaning supplies on hand at January 31.

How would I write this in a journal??

You don't write a statement in a journal. Statements are the summaries of what has gone on during an accounting period and the financial position of the company. You do those last.

You make entries in a journal.

As for yours, you need to have the balance prior to the entry. The count of supplies is what you have left. That is the amount that must be left in the account. The difference between what's in there now and the 210 is how much got used up.

What's used up gets expensed. Part of the definition of an expense is the consuming of an asset. You've consumed that asset so it gets debited to the supplies expense. And since you don't have them any longer, they get credited out of the supplies account.

That's a deferred expense, which all work the same way: debit the expense and credit the associated asset account.