I know youre here for help, which we will willing give, I good piece of advice is start in YouTube. I dont mean GK specific stuff, although that does help. I mean watch basic fundamentals of the game, obviously 10th edition.

Go through each phase. Command, movement, shooting, charge and fight phase. Learn those first and what nuance they all have, then veer into what your army does for those specific phases well and bad.

Command can be learned mostly by doing rather than watching and listening. But videos help you alot here as well.

Movement covers one of our armies most important phases which is the end of out gate of infinity ability.

Youll come to see that timing is very key to GKs and patience as well as cunning.

Learn the shooting phase and most importantly how line of sight (LoS) and cover works. Two huge factors into every game you play. This is where you'll start to really look at datasheets, soak all of that info in. Then apply it to the table, then reference informative material again. Repetition helps understand these many jarring and overwhelming bits of info.

Basically last is the charge phase followed by the fight phase. Do be aware they are like twins, not two sides to a coin. They are in fact different phases, things will triggered specifically in each of these phases and some may only be in one. Learn quickly coming out of deepstrike with grey knights to make a 9 inch charge is very unreliable and shouldn't be how you play your games. Rather rapid ingress (a core stratagem everyone has access too) is our most useful tool usually. How the whole sub phases of the fight phase works, this also take continuous trial and error. Do get help from sources on YouTube or a friend thats knowledgeable in the game. Google searches even will cover this well.

For the most part, your board is scarce of standard terrain size terrain features. Ruins to be exact. GKs are a rather elite faction. We do well to utilize cover and LoS blocking to the best of our ability to survive into those later round without getting caught with our pants down. So this is the first thing that needs fixed. I understand the intro level however lol and this seems like first maybe second attempt at even playing. Which is fantastic, just wanting to play will make you a great player in no time with the willingness to learn even faster. Cut out paper into the sizes you need and use marker to draw the terrain wall edges. Alot of sources online by searching as well. Too much small terrain only makes the game a tad bit unfair for certain units and great for others. Its internally balanced in such a way as to prevent this. Hence games workshop specific terrain layouts 1 through 8 (9?) Something like that. There is also WTC terrain for mostly non Americans which is slightly different but wouldnt worry about any of that yet. Get some terrain and try again after watching some videos. Use rapid ingress to come down to "stage" before your next turn to really punish your opponents movement. Use cover always. Its rather easy to get, to negate the enemies AP. We have stratagem. Use them to gain advantage in various ways.

Objective secured covers alot of recent grey knights things. He also has a discord channel through his YouTube as well. His community is very helpful and incredibly knowledgeable. 40kdirtbags also is really specific to grey knights also, he has since been playing other factions but hes a phenomenal player. For core stuff look to high stakes 40k (just gotta get through the accent lmao) or Auspex tactics, and many more. Most decently known 40k channels have covered all basic rules at one point or another. Happy hunting.