My friend has recently started using Marth and I can't even attack him with my falcon he always just Ftilts me or uses a fair and I can't even get close I've tried using SHL but he either counters or shields. when he goes in for the offensive I find that I can't even defend because if I block he will just grab me and if I don't then he'll just use a fair or ftilt I'd like to hear some of your advice on the MU and strategies I can use to beat him.
If he's constantly able to F-tilt and grab you with Marth, it means you're moving too slow and predictably. Go into Training mode and practice making your moves more unorthodox-like.
The thing I noticed with inexperienced Falco players is that they always SHL in-place or towards the opponent until they are in range for close combat. Pretend you and the other player are on opposites sides of a stage. If you SHL laser towards the other player, it's only natural that he/she will keep shielding, jump out of range, or take the hit while waiting for you to be in grab or counter range. I just recently watched a PM stream where a Falco player would keep using SHL towards a shielded Ganondorf. He would always end up being grabbed and punished. To solve your laser problems, go into Training Room (in Training mode) and perform your short-hop lasers from one side to the other. Keep doing this for 15 minutes, then take a break for 10, or you can choose how long you want to do it for. But practice this for one week. Once you master it, try wavedashing back after a SHL, then dash dance. You'll eventually develop your own style of doing this. Also, learn to fastfall your lasers.
Falco is not a character that's supposed to be on the defensive. You want him to control the stage. From what you said, if your friend is always countering or shield-grabbing you from SHLs, then you already have have half the stage set up. You just need to know how to approach. Practice doing SHFFLs into an immediate grab. The good thing about lasers is that they auto cancel, so there's no lag once you land. If you SHFFL and end up in front of your opponent, grab immediately. If you practice this enough, you'll be able to grab the other player while they are in hitstun from the laser.
Also, get used to not landing in front of the other player when you perform a short-hop aerial.
If you really want to get better, search "PM Falco vs. Marth" or "Falco" on YouTube. I'm sure you'll learn many things from watching others. Another thing you could do is post a video of your gameplay with your friends. We'll be able to help you as long as the video quality isn't potato.