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The size your UI is laid out at before it is scaled to each display.
Selecting and moving
Click an instance to select it (or pick it in Layers). Drag to move, and use its handles to resize. Shift/Ctrl-click adds or removes an instance from the selection, and dragging moves the whole selection together. Align, Space, Place and Smart scale act on it.
While dragging, smart guides snap to the centre and edges of the parent and of neighbouring elements (hold Alt to drag freely). Holding Shift moves in fixed steps instead; set the step in the hint bar. A child controlled by a UIListLayout/UIGridLayout can't be dragged directly: edit its LayoutOrder or the layout's own properties, exactly like Studio.
Keyboard
The view
The scroll wheel zooms toward the cursor (or pinch on a touch screen). Pan by dragging with the middle mouse button, holding Space, or one finger on empty canvas; Shift/Alt + wheel also pans.
Drag the small label in front of a number to scrub its value; Shift makes it 10 times faster and the arrow keys step it.
Animating
In Animation mode, editing Position, Size, colours, transparency and other numeric properties records keyframes at the playhead instead of changing the resting layout. Click the diamond beside a property to key it, drag diamonds to retime them, and pick an easing from easings.net.
Every animation becomes code: two functions near the top of the exported script, Animations["View"]["Name"].Play() and .Stop(), that you can call from anywhere. Tick Play automatically to start one when the UI loads.
Drawing
Draw is a small vector tool for making your own pictures. Pick a rectangle, ellipse, line or path, drag on the 512 × 512 canvas, then use Select to move a shape, drag its handles to resize it, or change its fill, stroke and width. Draw keeps its own undo history, separate from your design. Save to Library flattens the drawing, uploads it to your Roblox account and keeps it in the Library's Images tab, ready to put on an ImageLabel or ImageButton like any other picture.
Events
Select a layer and open its Events tab to make it react: when it is clicked, hovered, or (for a text box) focused, play an animation, go to another view, show or hide something, or run your own Luau. Choose the ScreenGui itself for When the UI loads. In your own Luau, UI.<name> reaches an element; the Insert an element list writes it for you.
Components
Select a button, a card or a whole panel and press Save selection as component in the Components tab (or right-click it). The layers inside come along, with their animations and events. Click a saved component to add it to the selected layer, as many times as you like; each copy is its own. To change one, edit a copy, select it, and choose Update from selection in the card's menu. They are kept in this browser, or on your account when you are signed in. Library icons come along by name, so they upload to whichever Roblox account exports the design.
Icons, textures and images
On an ImageLabel or ImageButton, Library opens 500 icons and 50 generated textures, plus My Images and Images, where the pictures you upload or draw are kept. A pick shows on the canvas straight away; with your Roblox account connected it uploads to your own account (once) and fills in the asset id. They are white shapes, so the image colour tints them. Textures that tile set the scale type to Tile.
Exporting
Choose how the script will run. Command bar builds the UI into StarterGui as real instances with a controller script for the animations and events: paste it into Studio's command bar and press Enter. LocalScript is a script for StarterPlayerScripts that builds the UI when the game starts.
Sharing
Sign in, then Share publishes a public link to a copy of your design. Anyone can look through every view, share it on, or open their own copy. Update shared copy refreshes it and Stop sharing takes it down. The panel shows how many people opened the link, saw its preview, and pressed a share button.