I've noticed a few different item descriptions that I haven't been able to find descriptions for, fragile sturdy and a number. Where could I find the rules for those?

I was also wondering when a mutation gives a +1 or -1 etc. modifier is that the same as increasing the die up one rank? like a d4-d6?

Hello! Thank you very much for reading through the game, hopefully you’ll get a chance to take it to a table. 

The Items you’re referring to are all Armour I believe. The number is the amount of Armour that item gives- Armour acts like a form of Health, reducing to protect Resilience, which itself protects the Wounded conditions. So Armour of 4 can absorb 4 Damage before it breaks. Armour can be repaired by certain Talents, using the Hacking skill. 

Fragile and Sturdy are really narrative descriptions, which can be interpreted by the GM at their table, but like the idea that Fragile items are impossible to repair if broken completely, whereas Sturdy items are easy to  repair (step the repairer’s dice up one, so d8 to d10 etc). 

And yes, the modifiers are exactly as you described- -1 skill means a Skill reduces by one dice, from d8 to d6 etc. The Skill reduced is agreed by GM and player through negotiation. 

Hope that all helps!