There are lots of tools I use in my sewing room but here are my top 5 must haves for any project. Any good Sewist will tell you the number 1 is a seam ripper! Yep that's right doesn't matter how long you've been sewing you will always need a sharp seam ripper near by to undo a mistake. I would think after all these years I wouldn't need it as much but when you do alterations you need it to rip apart a garment and then of course to rip out and re do something. You can find them at the fabric store, most craft stores, and Walmart and of course on Amazon. https://amzn.to/2zCwD1T
Second is a good pair of sharp dress maker scissors. I am partial to Gingher, they are well made and very sharp which what you need for fabric. Whatever you do remember don't cut paper with them! (Even though I have from time to time)
Third would have to be pins and lots of them! I like quilting pins because they are longer and have a round ball at the top which is easier to grab. I don't like those short little pins they are hard to work and the only use I see for them is pinning mens dress shirts for display. https://amzn.to/2NP9vQC
Number four is tailors chalk. There are various ones you can buy. I would stick with white because I just don't know how well the colored chalks can be removed and I don't work with fabric a whole lot to really need the colored chalk anyway. I do like the Carmel Super Glide Tailors chalk because it steams right off the fabric. It works great for marking alterations or pattern lines or info you need to transfer to your material. https://amzn.to/2zHwn1x
Number five is going be a hem gauge. While these are for measuring pants while you're fitting someone to hem their pants but they are super handy because they are small and you can grab it to measure a hem, seam width, etc. https://amzn.to/2ur3t0B
So as you get started with sewing these are the first things I would suggest starting with and then add to your collection as needed per project.
Let me know what some of your must have tools are.