The Ukulele is  a compact and small and relatively light instrument. You can play the Ukulele whilst sitting down or standing upright.  The main thing to look out for is to keep the Ukulele balanced and that you keep your hands free! Your Left hand is used for fingering the chords, not for holding or supporting the Ukulele. The Ukulele is supported by being tucked underneath your Right arm. Do not hold the Ukulele with your Right arm as it will prevent you from strumming effectively. Tuck the Ukulele underneath your arm, just let it rest there.
For strumming using your thumb (or first finger, or a Plectrum) of your Right hand. Strum the strings just above the fretboard not above the whole, (as what you would do while playing a guitar) playing in this manner will give you a stronger sound. Strum with a loose wrist, you can rotate your wrist slightly as you strum. All of this will become easier with time, avoid playing with a stiff wrist ( a common problem for beginners!) as it will  make your playing sound stiff as well!
Chords and single notes are being played with the tip of your Left hand fingers. All Four fingers are being used to finger chords, even your Pink. Try to stick to the “correct” posture and fingering right from the moment when you start as it will make playing easier in the future.

Have fun and hope to see you soon again,
Eddie