Hi! Welcome to SC1! 
I’m not a 1v1 player myself anymore, but even when I started playing years ago, I still felt overwhelmed but the weakest players.
If I were in the same position as you, I’d watch all these great videos made by our beloved Day[9], which cover the basics of Starcraft and a lot more:
After that, I’d check out this page, which presents a compilation of great Starcraft resources, put up together by TheEngineeringBay:
https://github.com/TheEngineeringBay/Starcraft-Community-Resources
Ultimately, I’d play against the bots created by the starcraftai.com community, using SCHNAIL, created by Sonko, found here:
https://schnail.com/#/home
SCHNAIL only works with Starcraft v 1.16.1, not with Starcraft Remastered. If you beat the hardest bot on SCHNAIL you are as good as a low B on the battlenet ladder, if I’m not wrong.
Here’s a video of the creator himself showing how SCHNAIL works:
You can also use https://repmastered.app/, made by icza, to get valuable replays of other players or to upload your own replay for analysis. SCRChart is also a nice tool for replay analysis, made by MasterReY, found here:
https://www.scrchart.com/.
I think repmastered works with replays from both 1.16.1 and SC:R, while SCRChart works only with replays from SC:R.