Mobile Suit Gundam: Battle Operation 2

First week

The first day you play, make sure you have a few solid hours before the daily reset (20:00 UTC)
Play through a few of the tutorial missions to get yourself comfortable with the basic gameplay
Visit the hangar and put a mobile suit in there. It takes forever to get anything out of it, and you can still play with the suit while it upgrades, so get started early
Make sure to jump into some quick matches and try to complete your daily missions every day for the first week - you'll get triple token rewards during that period
Eventually complete all of the tutorials, they give great rewards including some solid MS
Don't sleep on the simulator missions either, these give decent rewards and refresh every few months
And join an active clan. You'll get tokens and/or DP every time the clan levels up and completes missions, even if you aren't contributing much

Currencies

Tokens - These are what you use to "call a supply drop" (roll from the current gacha list of MS and weapons). These are earned through daily missions or bought with real money. Regular drops cost 3 tokens each; it's usually best to save up for "half-off 10" drops (15 tokens for 10 drops) that usually happen every 2-3 weeks, or for guaranteed MS step-ups
DP - You use these to buy MS, weapons, and custom parts from the supply depot. They're earned by playing missions. Items in the DP store or rank-limited.
RT - These are used for the RT store, and can purchase MS and weapons that are either not available in the DP store yet, or you are too low-level to buy. RT are usually gained by getting duplicates during a supply drop, and are the rarest of the currencies. Don't use them on things you can buy in the DP store.
Mechanic tickets and modification kits - These are for the hangar, worry about them later

Rank and rating

Rank is your level, and goes up with XP earned in every sortie. All it does is gatekeep availability of items in the DP store, and the ability to paint your MS
Rating, from D- to S, is used for matchmaking in quick matches and rated matches, but only increases or decreases in rated matches

Custom parts

Once you have a few suits across the various point levels (you can ignore anything below 200), focus on spending your DP on custom parts for a while. Every part only needs to be bought once, and can then be assigned to any or all of your MS simultaneously

MAS/Weapon level

Higher-level MS and weapons are basically disctinct items in the gacha inventory. So a level 2 Gouf is just a Gouf that costs 50 points more and has slightly-higher stats, that can be purchased or rolled separately from the level 1. For the most part, you'll always want weapons that are the same level as the suit, not higher or lower.