Most plants will not flower inside under regular shoplights. If you had special, full-spectrum (expensive!!) grow lights, you might could get them to bloom. But, once they move to sunlight, you should have blooms.

Sleepy is right. Most plants don't flower inside. They also don't usually flower until they are mature enough.

What kind of fertilizer do you use and how often do you use it. A fertilizer that is high in nitrogen--the first number on your fertilizer box-- will make lots of nice lush green leaves and few if any flowers. Use a balanced fertilizer like 15-30-15 or one that has all the numbers the same and only use it about every 2 weeks. Nasturtiums in particular don't need much fertilizer.

Don't feel you are alone. When I was a newbie, the first year I grew nasturtiums I had a lovely dark green bush of leaves and not one flower. Now I get lots of flowers. It's all about learning.