Welcome to this Forum. You may want to write a few lines about yourself in your profile. It sometimes helps if we know a little about the person we are responding to.
The standard response to a question like yours is something like,
Please attach a datasheet, or a link to one, so responders can give specific advice without hunting all over the 'net. (Many of us are on the Forum during work breaks or between school classes and don’t have a lot of time to hunt down background info.)
Don’t be such a wimp! The REAL PCB designers make their own symbols and footprints. They whip 'em out while riding the elevator up to their floor. OK - I’m just teasing the new guy because new guys always get teased. @John_Pateman gave you the kinder, gentler, more detailed version of this comment.
But in fact you have cited (probably by accident, but nonetheless relevant) two examples that are somewhat problematical and worthy of more detailed discussion.
The pressure transducer doesn’t seem to have a standard symbol that is widely recognized. Seed a search engine with " pressure sensor schematic symbol " and several possibilities show up, including symbols from the world of hydraulics and pneumatics as well as electronics. As a designer responsible for documenting your work, you may want to consider who will be reading the documentation in the future when you create a symbol. (Since this is is an analog, electrically resistive, sensor I would probably use some variation of a potentiometer symbol, with the text notation “Pressure”, or “PSI”, or “kPa”, etc. But I am an analog circuit designer at heart, not an industrial controls engineer nor pneumatic system designer.)
My superficial examination of that sensor’s datasheet indicates that the footprint for an 8-pin IC package - either thru-hole DIP or SMD SOIC, based on your part selection - should be suitable. The standard KiCAD libraries include several variations of those footprints, tailored to assembly methods.
The switch is problematical because, while it is functionally a TWO-terminal device, it has FOUR connection pins which are internally connected as pairs. The two extra pins eat up acreage on your board, but the internal connections can also be a useful resource to simplify routing. Unfortunately, KiCAD doesn’t understand components with internal connections so you usually get a DRC squawk when you try to exploit them. I think this problem shows up on the Forum a time or two every year; a recent thread is at " Tactile switch with internally connected pins ".
I drafted a custom symbol for tactile pushbutton switches like this, showing all four connection pins (plus the shield pin that sometimes connects to the switch’s mechanical frame). After I finish board layout, I modify the schematic to reflect the pin connections as I actually used them :
In addition to the sources mentioned by @halachal, there is an extensive library of KiCAD symbols, footprints, and 3-D models at http://smisioto.no-ip.org/elettronica/kicad/kicad-en.htm . You may also find small collections of KiCAD symbols and footprints in various Forums and Projects on the 'net. These can be valuable resources but you must DEFINITELY review them carefully before using them in your project. They are probably not fully compliant with the KiCAD Library Convention (KLC), and may have legal restrictions.