You can sow Myosotis sylvatica late summer through till end September, so not quite yet, but they won't flower this year even if you do plant them right now - they'll flower around May next year. They cannot be grown as houseplants. Sow where you want them to grow in the garden - they will tolerate full sun, but actually prefer light shade.
Bear in mind, though, they are commonly known as Forget me nots for a reason - once you've had a single plant in the garden, there'll be several the year after and even more ongoing, that's why they're hard to forget, so don't sow too many. If you want them to set seed and spread, don't remove the plants next year till the seeds have formed and gone, though usually, being prolific seeders, even removing them before they set seed still means there'll be loads the following year. You don't have to pull the plants out when they finish flowering, but they often develop mildew and look awful, so quite often many are removed.