If you don't think that you can sew, then now is the time to just do the best you can - your clothes will last longer and that is a very good thing for the planet (and for your bank balance).
Ask someone you know to show you how to sew, or turn to YouTube tutorials, or ask at your local haberdashery / sewing shop which local courses / sewing teachers they recommend.
Even if you 'just' (badly) repair a hole in your sock then you will have saved yourself money and kept an item in circulation for longer - a real step towards living less wastefully.
Things I've fixed / altered recently..
holes in the knees of jeans (patched on the inside with spare pieces of totally-past-it jeans)
bags for life which come apart at the seams
a straight scarf into a circular scarf (meaning I will wear it more, as it's now an easy option)
a necklace which had fallen apart
the length of school trousers
the width of PE jogging bottoms (so they no longer fall down!)
a torn cushion cover
the paw of a favourite soft toy
the bobble back onto a bobble hat
When just starting out on your sewing journey, please don't rush out and equip yourself with 'stuff' (certainly don't get one of those 'sewing kits' full of things you'll never actually use) - all you really need is a needle, some fabric scissors (yes you do need these, as cutting fabric or thread with 'normal' scissors blunts them), sewing thread and some pins (or just use the safety pins which often come attached to new clothes, for the time being) - if you graduate onto a sewing machine then look for 'flower head pins' which are flat and you can iron over them and sew right up to them. Most of these general items you can borrow from a keen sewer - they will definitely have a surplus of needles and pins.
You will need sewing thread - most comes on annoyingly plastic reels, but not all! Sewing thread is available on plastic-free, reclaimed-wood reels, from the greenfibres website. Of course it is always best to use up what you have, but when your next sewing thread reel runs out, do consider going plastic-free when replacing it.
If you do fall head-over-heels for sewing then you will most likely consider getting a sewing machine. But, always borrow one to try out first - preferably with the experienced owner sat at your elbow talking your through what to do. All sewing machine brands are very different and you shouldn't rush into buying one unless you have tested it and decided you really need it (and can fit it in your house) - me and my mum actually share a Singer sewing machine between us.
Sewing has saved me a fortune over the years - I've made / adapted curtains, cushion covers, pet bedding, garden canopies, lots of passed-on-to-me clothes and a really giant bean bag - if you do plan to sew a beanbag then it is worth knowing about the Eco Bean Bag company which sells compostable beanbag filling (rather than plastic polystyrene balls). Obviously this tip is just for those making a new beanbag, please don't replace something that is plastic but perfectly useful still.
Happy sewing!