Destiny

You will find Engrams throughout you journey in Destiny, they look at a glance the same as weapon/armour drops. Once you find an Engram you must go to the Tower and talk to the merchant on the right as you land to see about getting it Decrypted.

Considering this is a drop-based achievement this could take you a few hours to a few days. However if you buy engrams from the merchant I cannot confirm if they count towards this achievement. That said I would say from my experience it seemed to help.

*EDIT 1: You CAN buy engrams from the merchant for progress on this achievement. Thanks to Vermigs for confirmation *

If you're desperate for the achievement all I can advise is to go to a low level area (Earth, where the broken ship is to the north of where you land in Patrol is a good spot) and farm enemy kills. If you're a much higher level they'll fall like rain and you may get a few Engrams.

Hope this helps!

Also; for those having trouble unlocking glitchy achievement do this:

Press the Menu button RB over to settings, highlight Log Out and choose Switch Profile (not Change Character). This will take you back to the game start screen, and once you press A, it will ask you to choose your Xbox Live profile.

Choose your profile and then choose your character from the character select screen. Any achievements that should have been unlocked will then unlock.

*Cheers to FLEEBS & ludo10109 for the info

For me others achievements don't unlock (and for my friend this achievement too). If this happen go in the menu of destiny and choice to change the profile, now select again your profile. If you make this the achievements unlock.
Sorry the english is not my language.
Good play !

After collecting Engrams, you may want to consider holding on to them and decrypt them at a higher level/rank. Once an Engram is decrypted, it will scale to your current level. Thus, decrypting them at higher levels will mean acquiring better gear.

i.e., find an Engram @ level 15, decrypt it @ level 20 for level 20 gear. recommended for rarer engrams.

Here's my video guide for this as well as the 'Lucky 7s' and 'Use of Weapons' achievements

To get this achievement simply decrypt a total of 25 engrams. You can either play the game normally until you are awarded 25 engrams and then take them to the Cryptarch at the Tower to decode, OR, you may purchase engrams directly from the Cryptarch. Once your Cryptarch has decoded a total of 25 engrams the achievement will unlock.

*** DESTINY GLITCHED ACHIEVEMENTS FIX ***
Destiny Achievements are VERY glitchy. In order to unlock achievements
you have already met the requirements for you must cycle your connection
to the Destiny servers. The easiest way to do this is as follows;
ENTER the game > Press START > LOGOUT > SWITCH PROFILE >
CHOOSE your GAMERTAG > SELECT your CHARACTER > POP goes the cheevo

Hope this helps!
Happy gaming

-coreymawf