Back In The Saddle
One of Sarif's warehouses has been taken over by Purity First members - radicals against bio-augmentations in general. As recovered chief security, you're to handle the situation.
MEET WITH PRITCHARD IN THE TECH LAB [150 XP]
GO TO THE HELIPAD [150 XP]
After the full motion cutscene you're good to go. You now have two prosthetic arms, legs, several implants and a - glitchy - HUD; your first objective is to fix that display. Jensen furthermore starts the game with 2500 credits and 120 XP.
It's a good idea to talk to the receptionist, Cindy Martinez, whom you can ask for directions. She'll tell you where Pritchard's office is, as well as the locations of the helipad, Sarif's penthouse, and your own office.
While you're free to roam the area, do be noted that time *is* limited. After 7.5 minutes, David scolds you and tells you to hurry up. After 15 long minutes he tells you something bad happened (which can, of course, never be undone. This has consequences (for rewards, etc)).
You can find Frank Pritchard in the security tech lab, but first youmight want to speak with one of the employees on the ground floor, who are having a conversation about you. It doesn't really matter which answer you pick, and you'll get to hear some background information.
Also consider eavesdropping on the the woman at the women's restroom. She apparently knows something that you don't. In either case, head up the big stairs and go inside the Technology Lab (which is on this floor) to meet with Frank Pritchard. You'll have the option to either ignore or confront Pritchard with his attitude. The net outcome matters little in the grand scheme of things, but confronting him prolongs the conversation and gives you more details on Jensen. [150 XP]
The first [HUGH DARROW EBOOK] you can find in the game lies on Pritchard's Desk (The Nature of Neuroplasticity). There are a total of 29 in the game, and finding them all is worth an achievement/trophy. They also give 200XP each, granting a very nice total of 5800XP if you find and read them all.
Be sure to snatch the [CYBERBOOST PROENERGY BAR] from his desk, as well as the [91 CREDIT CHIPS] from his bench. And if you have a second, take a look at the poster of Final Fantasy XXVII (an obvious wink to Square Enix). Prichard's arc of old monitors is also worth looking at.
While there are, technically speaking, a few more things you could do right now (such as getting minor items), time is running short, and you'll have more time for exploration when you come back to HQ. Go to the far side of the second floor and head through the double doors. Take a left turn to reach the helipad, where Faridah Malik is waiting for you. After conversing, hop onto the heli to get your debrief from David. [150 XP]
The manufacturing plant has been invaded by radicals who call themselves 'Purity First'. Their leader is named Zeke Sanders, who appears to be in the plant as well. David gives you the option to go for a lethal or non-lethal approach, and either a short-range or distant combat style. These options affect which weapon you receive from David, so choose very carefully. It would've been boss to tell David to "Give me the GEP Gun", but alas, the below choices will have to do.
Nonlethal Short-range = [Stun Gun] 
Nonlethal Long range = [Tranquilizer Rifle] [9 Tranquilizer Darts]
Lethal Short-range = [Revolver] 
Lethal Long range = [Combat Rifle] [20 Combat Rifle Ammo]
While this guide provides you with adequate strategic advice for any of these weapons, it has to be said that the Tranquilizer Rifle is not only silenced (allowing for stealthy and nonlethal takedowns), it's also quite rare and expensive.
Jensen's standard equipment furthermore depends on any DLC and pre-order bonuses you may or may not have gotten. In any case you'll be able to play the game without any problems; some items just make things a little easier for you.