A weed! What's the soil like there? It's a bit difficult for us UK-based gardeners as conditions here are quite different. You could consider growing some native wild flowers to help local wildlife. I found this site which describes which native wild flowers grow in various regions of Bangladesh, if you're interested:https://en.banglapedia.org/index.php/Wild_Flower
The conditions and the plants that grow where you are in Bangladesh will be very different from here in the UK. Look around you to find the commonest plants in gardens or green spaces, the ones there are lots of. They will be the easiest ones to grow, but they will probably be ones you call weeds. They might be precious and difficult to keep alive here
Nasturtium is seed is big and it's easy to identify the seedlings.Poke your finger half way down into the soil, drop the seed in, cover the hole with soil, water and stand back.