At the start of your game, your stash will be given only a few starting items. On your equipment side of your inventory you will have a secure container. Depending on what edition of the game you purchased, your container will either be 2×2, 2×3 or 3×3. Everything you put into this container will not be lost when you enter a raid. I recommend putting Keys and medical items into it. Speaking of losing things, when you go into a PMC raid, everything you take in with you will be lost if you die. That is unless you INSURE your items, which you will get the option to before loading into a raid. insuring your items means that if no one has picked it up at the end of a raid, it will be returned to you after around a day. I recommend insuring most of your gear, as to cut your losses. In escape from tarkov, you have 2 raid options. A scav raid, and a PMC raid. A scav raid means you will spawn later into a match with a randomized set of gear, while a PMC raid means you will spawn in with the gear you equipped at the main menu. The first thing you'll want to do in tarkov, is hit the escape from tarkov button, click PMC, click customs, click a time that is in the middle of the day (e.g 1PM), click ENABLE OFFLINE MODE so you dont lose your gear or encounter other players, click enable PVE, click next, and then click ready. You will then load the map and be placed in an offline raid. Here you can learn the map, practise PVP with scav AI, and also figure out where your EXTRACTION points are. Extraction points are a very important mechanic in tarkov, as you cant just click leave and exit the match with all your gear. Extractions are usually placed at different corners on the map depending on where you've spawned. I recommend looking up "customs map tarkov" and getting used to the layout before playing an actual raid without offline mode.
Once in an offline raid mode, practise some of tarkovs more in depth mechanics. Tab to check inventory, X to prone, Q to lean left, E to lean right, C to crouch, middle mouse wheel to change how fast and noisy, or how slow and quiet your going, Aim + Alt to stabilise your weapon aim, O to check amount of time left in raid, Double O to check what your extracts are, G to throw a grenade (If you have one in your rig or pockets), Caps lock to instantly slow down, Alt + E to side step right, Alt + Q to side step left, Double tap Y for voice commands, Middle mouse click to instantly inspect an item, Control + click to instantly transfer an item to your inventory, Alt + click to instantly transfer a Bag, Weapon, Rig, or piece of armor to an empty slot, Alt + T to check your weapons magazine, Shift + T to check your weapons chamber, Page up and page down to adjust your weapons zero'ing (only works with scopes or sights), Double tap Z to quickly throw your bag (useful when overweight and cant run).
Once back in the main menu, look at your hideout. Your hideout is your base of operations, and in the future can be turned into a money making machine. As a new player, i'd recommend not paying too much attention to the hideout until you've unlocked the flea market at level 10.
On the "Trading" button on the main menu, check each one of your traders tasks to see if they have a quest available for you. Quests are a big part of EFT and reward money, experience, skill points, weapons, armor, containers, etc.
Once you have familiarised yourself with the customs map, go to escape from tarkov, scav, customs, pick a daylight time, and click ready. Scav players have different extracts to PMCs' so you will have to learn them separately. Scavving on maps is a good way to make money, and also a good way to get PvP experience. Your Scav XP however does not go toward your PMCs experience, so i recommend doing scav runs more infrequently than PMCs.
One thing you will have to also familiarise yourself with is the tarkov ballistic system. In short, Armor classes vary from 1-6, 1 stopping only buckshot rounds, and 6 stopping most rounds excluding armor penetrating rifle rounds. For a more detailed explanation go here:
Durability is a big factor in armors, meaning that if a low penetration round were to be kept shooting at a peice of armor, it would naturally degrade and give the round a higher chance to penetrate. Armor that is zero'd is completely useless until you repair it in your stash.
Flesh damage is also a factor in rounds, such as having a 9×19 bullet that has no penetration but high flesh damage. This means that if someone were to shoot an unarmored body part with a high flesh damage round, it would be more devastating than if they shot with an armor piercing round.