Depending on your climate, about seven days later, the seed will germinate and start to grow. It will get to the stage where you have two smooth leaves on each side of the stem. Then, true leaves will form that will be crinkly, like tomatoes leaves. Never let your seedlings dry out, but don't over water them and make sure they have good drainage. If the tray is kept wet it may encourage fungal disease. One watering a day should be enough but if you're in a hot climate, you should check them in the afternoon as well and give them a little drink if the soil is dry.
You can pick tomatoes green without it affecting their taste. Tomatoes ripen due to the warm air, not sunlight, so harvesting your crop green and ripening in the warm air on the veranda or on the kitchen window sill will give you excellent tomatoes. We also harvest our tomatoes green because in our main growing season there are a lot of bugs and birds just waiting for a nice ripe tomato to feast on.