You will not get any fruit from the plant on a window sill.
You can harden it off now and grow it out doors or put it in the conservatory or similar situation, indoors. It Will need at least a bucket full of compost to grow successfully!!
At the junction of the main stem and a leaf will grow a side shoot and these when about 2 inch long, should be removed. After about 4 leaves and between the leaves (inter node), will grow a truss. This is the fruiting part of the plant. Once the truss has formed it will bear flowers. Spray these , lightly with water. Remove ALL leaves below the truss. Continue winding the plant around the string and stop the plant after 5/6 trusses have formed. Stopping involves cutting the stem above the leaf above the top truss.
You are looking to have a single stem with NO side shoots just leaves and trusses. Any superfluous growth weakens the plant and means small fruit.
Feed once per week with "Tomarite".
If you haven't grown Tom's before you will be surprised how easy they are to grow.
Remember, no leaves below the trusses.
There is a need to pollinate the flowers and fine spray will help or use a fine brush or rabbits tail.
If outdoors fly and bees will do this.
Good luck.
Chris