The water has to drain from the bottom, otherwise it will pool up and cause all sorts of problems for your plants. You can buy some long plastic pots, drill holes in the bottom, and put some plastic covers on the bottom to catch the water as it drains. There are some wonderful round plastic pots, that have a bottom water collection tray that's removable.
Any store that sells garden supplies will probably have some sort of center set up during the spring and summer months, and most of them sell a wide variety of flowers, fruits, and veggies. If you'd rather plant seeds, follow the instructions on the package as each plant has its own unique needs.
As for flowers, choose a variety that does well in partial shade. If you have pets, especially cats, make sure your plant isn't poisonous! Tomato leaves are poisonous to cats, so have the plants in a hanging planter they can't reach.
Step Five - Place in Window
If you have a south or east facing window, place your plants there. If your only choice is a north facing window, you may need to supplement the little sunlight you do get, with a grow light of some sort. Keep your windows open for ventilation, or to ensure your plants get proper airflow, use an oscillating fan set on low or medium.