Explanations here are possible but you might want to click on the Glossary link above and explore. The abbreviations are listed there and some are linked to videos. Suzeeq explains things much better than I can.
P2 tog is a decrease
K2 tog is a decrease
yo (yarn over) is an increase
If you make a yo and increase there must be a decrease to balance it and vice versa.
Can you link to it? I don't know what instagram is.
You can't knit the left sock first. Ever.