ax = gca returns the
handle to the current
axes for the current figure. If an axes does not exist, then gca creates
an axes and returns its handle. You can use the axes handle to query
and modify axes properties. For more information, see Axes Properties.

x = linspace(0,10);
y = sin(4*x);
figure
plot(x,y)

Use the gca function to get the handle of the current axes. Then, set the font size, tick direction, tick length, and y-axis limits for the current axes.

ax = gca; % handle of current axes
ax.FontSize = 12;
ax.TickDir = 'out';
ax.TickLength = [0.02,0.02];
ax.YLim = [-2,2];

The current axes is the target for graphics
output. It is the axes in which graphics commands such as plot, text,
and surf draw their results. It is typically the
last axes created or the last axes clicked with the mouse. Changing
the current figure also changes the current axes.

User interaction can change the current axes. If you need to
access a specific axes, store the axes handle in your program code
when you create the axes and use this handle instead of gca.