I cannot emphasize the importance of starting small. Its crucial that you start small. I always say it in my Gardening Workshops, start with just one or two plants, maximum three. No more than three.
Flowering plants are the best ones to start with as they require very low maintenance. Also, they give us lot of scope to learn.
The plants need to be watered regularly (daily). Different plants have different water requirements. Excessive watering creates equal stress on a plant as inadequate watering.
Spend at least 2-3 minutes with your plants everyday.
Now, once you have been looking after your plants everyday, now add to your Garden every month. Buy 2-3 plants every month. Slowly build a Garden. Enjoy the process.
Keep it gradual and casual.