Aligned flowchart boxes

A flowchart looks amateurish for exactly one reason: boxes that almost line up. TikZ avoids the problem structurally, because every box is placed relative to another, so a column of boxes shares an axis by construction instead of by eyeballing. The second ingredient is a named style, so all boxes agree on their shape and minimum size. Here is a vertical three-step flow:

\usetikzlibrary{positioning,arrows.meta}

\begin{tikzpicture}[
 box/.style={draw, rounded corners, align=center, minimum width=2.8cm},
 node distance=10mm and 14mm
]
\node[box] (i) {Input};
\node[box, below=of i] (p) {Process};
\node[box, below=of p] (o) {Output};
\draw[-Latex] (i) -- (p);
\draw[-Latex] (p) -- (o);
\end{tikzpicture}

Defining a style once

The box/.style={...} line creates a reusable style named box. Its contents are ordinary node options: draw gives the node a border, rounded corners softens it, align=center centers multi-line text inside the node, and minimum width=2.8cm forces every box to at least that width so short labels do not produce shrunken boxes. From then on, \node[box] applies the whole set. When you decide the boxes need a fill color or a larger width, you change one line and the entire chart updates, which is the difference between a diagram you maintain and one you redraw.

Spacing in two directions

node distance=10mm and 14mm sets the default gaps used by the positioning library: the first value is the vertical distance, the second the horizontal. With that in place, below=of i places the process box 10 mm below the input box, edge to edge, and perfectly centered on it. A second column would use right=of p and land 14 mm to the side. Because each placement chains off an existing node, inserting a step means adding one node and updating one below=of reference, and everything downstream shifts with it. You can also override the distance per node, as in below=15mm of i.

Connecting the steps

Each \draw[-Latex] (i) -- (p); draws an arrow from one named node to the next, with -Latex selecting a solid arrowhead from the arrows.meta library at the destination end. The arrows connect at the node borders automatically. For a decision branch, draw from specific anchors, for example (p.east) to leave from the right side, and route with bends such as -- ++(2,0) |- once the chart needs corners.

TikZ output does not render in these in-page previews, so compile the snippet to see it. The classic mistake in flowcharts is placing a few boxes with absolute coordinates “just this once”: those boxes are the ones that end up misaligned after the next edit. Keep every placement relative, and see nodes and arrows for the underlying placement options.