with the krayt pearl it has a basic mod of dmg. 9, crit. 1, breach 1, sunder, vicious 1

and additional mods of 3 vicious +1's, and 1 dmg. +1

how do i activate the additional mods is it through advantages? if so how many

You mod attachments through a Mechanics check. There should be a sidebar near the start of the Attachments section that explains how it all works. Force-users modding crystals in their own lightsabers get to add their Force Rating (that's on a sidebar, I believe where they start talking about lightsaber crystals).

yea i saw that attachments like kybers can have force rating added and used to spend S or A with a mech check of 3+previous mods-2 but what i want to know is how to trigger the additional mods like curved hilts defensive quality or the krayt pearls additional vicious quality

No, really, it's at the start of the section "Customization and Modification" (p.192 for the Force and Destiny Core rulebook, for example). For the first mod, you need to pass a Hard Mechanics check, and for any further mods, the difficulty is increased by 1 per successfully installed mod. Failure means you fail to install the mod and may not attempt to do so again (though, if there are multiple mods of the same type, you may still attempt to install the other mods of that type), and rolling Despair on top of that means you break the attachment in the process.

Okay whats the difference between applying an attachment and making a modification

As for the effects of the mods, once you've installed them, they don't "activate" (unless they provide a Quality, or add to an existing Quality which needs to be activated, which is activated as normal per the rules for activating Qualities, typically spending a varying amount of Advantage based on the Quality in question.) "Vicious" just adds to d100 roll for determining a Critical Injury: A Vicious 1 Quality always adds +10 to the roll when you inflict a crit, Vicious 2 always adds 20, and so on. Increased Damage just adds to the weapon's damage, Decreased Crit reduces the amount of Advantage you need to spend to inflict a crit, and so on.

This is all in the basic equipment rules.

1 minute ago, Stormbourne said:

Okay whats the difference between applying an attachment and making a modification

An attachment is an item you add to a piece of equipment to improve its function. A scope for a blaster, let's say.

A mod is something you can add to the attachment itself to improve its function even more. In the example of the blaster scope, you may be able to tune it by increasing degrees to improve it beyond its stock effect, adding additional Accurate Qualities, for instance.

Not all Attachments have Mods available, and each Attachment will list the Mods it has available, and how many of them. If a scope has 2 Accurate mods and 1 Decreased Crit mod, you can't add a mod that increases damage, or reduces crit by 2.

Any checks for installing attachments

Check this thread: https://community.fantasyflightgames.com/topic/89135-another-character-generator/

It's a great character generator program that has all the rules coded into it. You can experiment there with the various equipment rules, adding attachments and mods, and even crafting gear (though without access to the various rulebooks its based on, some systems will be more difficult to understand). But it handles all the "math" on its own behind-the-scenes, so you can get a feel for what things actually do. That might help you get a grasp on the mechanics, seeing the end results and working backwards through how they came to be that way.

Accidentally posed this in your other thread, meant for it to go here. Sorry.

Yes, you need to make a Mechanics check to add Mods to Attachments, and the check increases in Difficulty per Mod the Attachment already has.

All good

45 minutes ago, Stormbourne said:

Any checks for installing attachments

There's no check needed to install attachments, except when called for in the attachment description (the Wookiee bowcaster attachments, for example). You usually only need to make checks to mod the attachments after installing them.