Due to how the in-game store works, this item might as well be titled “Praying to the Random Number Generator”. You earn credits by playing, then spend them on “packs” that are priced according to the probability that there’s something good in them, while the Common, Uncommon, Rare and Ultrarare characters, weapons and gear are aptly named according to probability of appearing when you open the packs you bought.
In the picture is a typical yield of the Premium Spectre Pack (the Common items are blue, the Uncommon silver, and the Rare – gold; the Ultrarares come on highly coveted black cards), at the price of 99000 credits. You can make around 80000 in a typical Gold, and around 120000 in a Platinum match. The catch is, you need to open literally hundreds of these (which translates to tens of millions of credits and likely at least a thousand hours of gaming) before, by the grace of the RNG, all your characters, weapons and gear are finally at their maximum level.
So yes, the infamous endeavor of Maxing One’s Manifest is as much of a pain in the ass as it sounds. It involves perpetually scraping for credits and consumables (which are found in the cheapest packs that come with virtually no chance of unlocking anything of importance), having your high hopes repeatedly crushed by packs containing nothing but crap, and piling up useless equipment (power efficiency modules and cryo ammo, anyone?), while getting increasingly desperate since, the closer you are to having that last pair of black cards revealed, the RNG seems the more determined to troll you.
But eventually even scrubs such as myself get it done.