How do I accrue the interest?

An accrual is something where the expense has been incurred but has not been paid yet. If you're accruing interest, it's because you're at the end of an accounting period and the interest that has built up so far needs to be recognized on the books as an expense. So you're debiting Interest Expense. Since it has no been paid yet, you're crediting Interest Payable.

All accrued expenses will have this same entry, except you substitute in the appropriate name. (i.e. Salaries Expense & Salaries Payable, Income Tax Expense & Income Tax Payable, etc.)