In TikZ, if you have a node like
\draw (0,0) node [] {My text};
you can add a border around it by using the draw=... attribute for the node:
\draw (0,0) node [draw] {My text};
You can also tell TikZ to draw it in blue:
\draw (0,0) node [draw=blue] {My text};
or tell it to draw it dashed:
\draw (0,0) node [draw, dashed] {My text};
You can also make the border thin or thick:
\draw (0,0) node [draw, very thin] {Very thin border};
\draw (0,-1) node [draw, thin] {Thin border};
\draw (0,-2) node [draw, semithick] {Semithick border};
\draw (0,-3) node [draw, thick] {Thick border};
\draw (0,-4) node [draw, very thick] {Very thick border};
\draw (0,-5) node [draw, ultra thick] {Ultra thick border};