Welcome to the forum!
As we often find, with Inkscape, there may be many ways to draw a particular object or image. So this is how I would approach it. But other people might come up with different or even better ways.
The other thing I often find, is that explaing how to do something takes 10 times longer than just doing it. So don't be afraid of all the text. Just read, and you'll get there. Or else, if you're not concerned about precision, there really are very fast ways to do this. Jump to the bottom for an example.
I'm not clear if you want the white space to be the same width as the black space. In your example, the black is a little bit wider. Well, this way will make them equal but you can see how to easily make them not equal.
- View menu > Page grid
- Set up Snapping -- click these buttons on the snap control bar (usually on the right side of the window)
- Enable snapping
- Snap nodes, paths, handles
- Snap cusp nodes
- Snap smooth nodes
- Snap to grids
- Disable all the other buttons except for those. (Snapping is like magic, and one of the best tools Inkscape has for precision.)
- Enable the Pen/Bezier tool.
- Because of snapping, wherever you click with this tool, it will put a node precisely on a grid intersection
- Click once on the canvas to start the new path, and click once at every corner, while you're drawing something that looks like a printing capital E, like in the attachment below (tr1.png)
- When you're coming back around to the place where you started, be sure to put the mouse inside that tiny square. It will get bigger and turn red, when your mouse is in the right place. Then click once, and that will end and close the path. The path has to be closed for this to work.
- (You won't see those tiny gray diamonds, like in my screenshot, which are the nodes, until you switch to the Node tool. However, you don't need to switch, for this process.) (Actually I was using the Node tool to adjust my giant E, because I didn't get it quite right when I was drawing it. So you can use the Node tool to do the same thing. Or you can use it to make the lines not equal - just drag nodes and they will automatically snap to the grid.)
- If you want, you can draw your triangle right on top of that, with the Pen tool, like in the next attachment (tr2.png) Or you can use the Star tool, and set it for Polygons, with 3 spokes. Then after you draw it, use the Selection tool and drag it over to the giant E.
- When it's in the right place, click on some ridiculous color chip in the palette, such as neon green or pink. (this is not absolutely necessary, but can be helpful to prevent confusing it with the other triangle, which you're about to make.)
- Duplicate it (this button on the command bar
) - While it's still selected, click on the White chip on the palette
- While still selected, move it to the bottom of the stack (this button on the control bar
) - Using the Selection tool, click either the giant E or the pink triangle, hold the Shift key, and click on the other (the Shift key makes them both selected at the same time)
- Path menu > Intersection
- Now you should have something like the 3rd screenshot (tr3.png)
- While still selected, click the black chip on the palette
- With Selection tool, drag a selection box around the whole thing (this selects both the stripes and the white triangle underneath) (a selection box is easier when objects are stacked on top of each other - but you could hold Shift and click once on each one - whatever you prefer)
- Object menu > Group, or it's this button on the command bar
- If it's still selected, click on it once to see the arrows change (if not selected, click twice, slowly, not as fas as a double-click)
- Hold the Ctrl key, and grab one of the corner arrows. Drag through several steps (the Ctrl key makes it move in 15° steps - without Ctrl, it's harder to be precise)
- I think it's 8 steps to get it rotated to the way you showed in your example
So that should be it.
To do it without precision:
- Draw a horizontal path (Click with Pen/Bezier tool, move mouse to the side, double-click to end)
- Make it really wide, so it can be a stripe (Object menu > Fill and Stroke > Stroke Style tab > Width)
- Path menu > Stroke to path
- Duplicate
- Move it down a bit
- Duplicate
- Move it down a bit
- Duplicate
- Flip it 90° (either one of these buttons on Selection control bar
or 
) - Move to either side of the 3 horizontal bars, making sure it overlaps all 3
- Select all 4 (drag a selection box or hold Shift and click each one once)
- Path menu > Union
- Draw the triangle and put it in position, make it white
- Go to #13 above, it's all the same from there
And I can still think of several other ways to do this. I wouldn't be surprised if I left out a step, since I'm writing in a hurry
But in any case, let us know if you have questions or get stuck.
