I'm casting a wide net here with this post.

I'm interested in participating in some type of competition shooting eventually doing 3 gun but I have no idea where to start.

I'm an experienced recreational shooter and I've taken carbine and pistol classes in the past. I'm located in Monterey CA.

Thanks in advance for your help!

Find a club or clubs local to you that put on what you're interested in.  Many clubs on my side of the country rotate IDPA, USPSA, 3/multigun and steel challenge.  Go and observe a match or matches.  I prefer USPSA for pistol shooting.

Study up on the rules and divisions.  For example, USPSA has open, limited, production, single stack, L10, carry ops and PCC...each has it's own rules on the type of gun and equipment you can use, power factor for the ammo, etc...i.e. production division allows Striker and DA/SA pistols, but not SA pistols, and all equipment (holster/pouches) must be behind the hip bones.  Open and limited will have more relaxed rules.  Since you're in CA you're probably going to look into Prod, SS, or L10.  Almost any type of iron sight gun and holster/magpouch combo will fit into L10 rules.  

Go and shoot one.  Clubs around here are used to and inclusive of new members.  Learn the safety rules and commands, have fun and don't DQ.

Do not buy gear. It's likely you'll get incorrect thing. I bought a bunch of gear that all of the good guys had once I decided I was going to make a commitment. I shoot highpower And there's more junk to buy than I ever imagined. I n highpower you can go to a clinic, or small arms fire in school SAFS For very little money. If you get gear now it may not fit you, even though it works great for someone else.

If you can find a local steel match, go try that first. There is no requirement to draw if you shoot .22
You would only need a .22, 6 magazines that hold at least 6 rounds (or 6 speed loaders), eye and ear protection, 150 - 200 rounds of ammo and a carry case/rug for the pistol.

You could also look for a USPSA match or IDPA match local. Look at their web sites for affiliated clubs in your area. If you are not a little practiced in drawing a handgun, moving with muzzle control, and reloading under a little pressure, I strongly suggest you watch one first and maybe practice those skills a little before trying to shoot a match. You do not need to be really fast at any of those things, you just need to be really safe doing those things under pressure.

I started by showing up at a local gun club that had regular IDPA matches with my Sig P228, a holster, a few mags and a lot of questions.  Even though I have shot recreationally a ton, and had a bunch of years in the military I left the ego at home and took it slow and asked a lot of questions.  Since then I've shot a bunch of different types - IDPA, USPSA, 2 & 3 gun and had a blast.  Met a lot of great people and have always (in several clubs and even states) seen first timers treated VERY well.  Shooters love introducing others to the sport.  The toughest part is just showing up for the first time.

Biggest tip I like to give first timers - After you fire you last shot on a stage, take a deep breath and relax.  The timer stops on your last shot. so calm down (as your heart will probably be pounding) get your composure, and let the RSO talk you through clearing your weapon.  No need to hurry here.


Have fun!

https://uspsa.org/ use the Find a Club feature halfway down the page.  It has contact info for match directors of your local matches.  Contact them and let them know you're new to competition and want to shoot one of their matches.  Some clubs offer new shooter briefs and things like that prior to matches, so the match director will give you that info.  Take a read through the rulebook so you understand basic rules and equipment requirements.  There's probably some intro videos on youtube as well.

Obtain lots of ammo, and mags for practice, and competition. Do not be bothered by stuff like required dropping of an empty mag in the grass during competition as you insert a full mag.

Study the rules- do's and don't in great detail. Watch top competitors during their turn for timesaving, or expert techniques.

When you have particularly internalized gun safety, you can begin speed drills and think about what really separates top competitors from the rest of us. Not only accuracy, I'm talking about the way you move every step of the way, moving and shooting around corners, etc.

Examples:shooting from behind fake blue mailboxes, sitting in a car while shooting out the wndows on the range, and other cover while dropping empty mags and reloading the next one.

Take what you have and go shoot.  The good ones will help you all you want.  Ask questions.  

I’ve seen some less friendly ones get their asses handed to them for not being welcoming to the new guys.  They have a tendency to shut up from there.