The linear kernel is what you would expect, a linear model. I believe that the polynomial kernel is similar, but the boundary is of some defined but arbitrary order
(e.g. order 3: ).
RBF uses normal curves around the data points, and sums these so that the decision boundary can be defined by a type of topology condition such as curves where the sum is above a value of 0.5. (see this picture )

I am not certain what the sigmoid kernel is, unless it is similar to the logistic regression model where a logistic function is used to define curves according to where the logistic value is greater than some value (modeling probability), such as 0.5 like the normal case.
Answer from John Yetter on Stack ExchangeVideos
The linear kernel is what you would expect, a linear model. I believe that the polynomial kernel is similar, but the boundary is of some defined but arbitrary order
(e.g. order 3: ).
RBF uses normal curves around the data points, and sums these so that the decision boundary can be defined by a type of topology condition such as curves where the sum is above a value of 0.5. (see this picture )

I am not certain what the sigmoid kernel is, unless it is similar to the logistic regression model where a logistic function is used to define curves according to where the logistic value is greater than some value (modeling probability), such as 0.5 like the normal case.
Relying on basic knowledge of reader about kernels.
Linear Kernel:
Polynomial kernel:
Radial basis function (RBF) Kernel: which in simple form can be written as
Sigmoid Kernel: which is similar to the sigmoid function in logistic regression.
Here ,
, and
are kernel parameters.