Mods can make alterations to your computer or minecraft instance, so google will often worn you when downloading them. However, all mods on curseforge are checked for viruses before being uploaded, so you should never have to worry when downloading here. However, that is not always the case on other sites, so be careful!
Cauldron is a a program that edits minecraft, similarly to minecraft forge, except it is able to load forge based mods and bukkit plugins at the same time (for a minecraft server). It is apparently very hard to set up and use, but I have never done so myself.
One of the more than 140 mods in my custom private modpack (1.7.10) is adding a indicator next to my cross hairs showing what status effects I currently have. This is supposed to be helpful, but I find it irritating and distracting. Does any one know what mod adds this, and how to turn it off?