The primary way of editing code in Pharo, Squeak, and similar implementations derived from Smalltalk-80 (but not all, some use the more familiar idiom of "many files in many directories") is to use one of the built-in (to the Smalltalk environment) browsers.
Select the package, class, and then method (or the options to create new ones) and the method will be in an editor pane for you. Start changing it, and the change is immediately applied once saved. No need to rebuild the world and restart the image. (Of course, that leads to some fun things where you can redefine True/False and break the image right there on the spot. Pharo seems to do a good job of blocking you from changing things like that so easily.)
Smalltalk code "lives" in a database. You interact with that database. The code is also serialized to a file if you happen to want more conventional access, but that's not the normal route. Though serialization to files is how Pharo and others allow you to interact with git and collaborate with other people.
Select the package, class, and then method (or the options to create new ones) and the method will be in an editor pane for you. Start changing it, and the change is immediately applied once saved. No need to rebuild the world and restart the image. (Of course, that leads to some fun things where you can redefine True/False and break the image right there on the spot. Pharo seems to do a good job of blocking you from changing things like that so easily.)
Smalltalk code "lives" in a database. You interact with that database. The code is also serialized to a file if you happen to want more conventional access, but that's not the normal route. Though serialization to files is how Pharo and others allow you to interact with git and collaborate with other people.