Use braces instead of parentheses:
% Create sample data.
v1 = sort(rand(10, 1))
v2 = rand(10, 1);
t = table(v1, v2);
% Plot column 2 vs. column 1.
plot(t{:, 1}, t{:, 2}, 'b.-', 'LineWidth', 2);
Braces get you the contents of the table. Parentheses get you a 1-column table, not a 1 column vector of doubles.
