Photoshop on the web vs the desktop app
Adobe now ships Photoshop in two forms: a browser version that needs no installation, and the full desktop application. They are not interchangeable.
Short answer
Photoshop on the web runs in your browser and covers everyday edits — cropping, retouching, layers and quick object work — without installing anything. The desktop app remains the full version: every tool, every filter, RAW development, plug-ins and offline work. Start with the web version for light tasks; install the desktop app when you need the complete toolset.
What the web version does well
Photoshop on the web opens at photoshop.adobe.com and works in a current browser. It handles the tasks most people open Photoshop for: combining images on layers, removing backgrounds and objects, adjusting colour, and exporting for web use. Because nothing installs, it works on locked-down machines — school laptops, work computers, Chromebooks — where the desktop app cannot go.
Documents sync through your Adobe account, so an edit started in the browser can be finished in the desktop app and vice versa.
Where the desktop app is still necessary
The web version is a subset, not a replacement. Camera RAW development, advanced masking, the full filter library, actions and automation, plug-ins, print preparation with colour profiles, and working without an internet connection all belong to the desktop application. Professional and print workflows assume it.
The desktop app is also demanding: check the system requirements before starting a trial on an older machine.
Access and cost
Adobe ties both versions to the same account, and what you can use depends on your plan and Adobe's current offers. The free Photoshop options page tracks the legitimate free routes; the desktop app itself is available through the seven-day trial or a subscription.
How to decide
One question settles most cases: do you need the tool, or the task? Cropping a photo, removing a background, combining two images — the browser covers these in minutes with no install. Retouching for print, building layered composites with plug-ins, developing RAW files — that is desktop work, and no web version changes it.
On Windows, see Photoshop for Windows; on Apple hardware, Photoshop for Mac.