'Work done by a varying force' question

I just reached this part of the textbook and I am given a formula that looks like this,

W = ∫ab F*dx (the a is supposed to be at the top of the ∫ and b at the bottom)

I do not understand this part in my textbook. What is the ∫ ? I thought it had something to do with Integral Calculus but I haven't taken it yet. Only Differential Calculus. Can anyone explain this formula to me please? It would be very much appreciated!

W = Integral[x=a,b; F.dx]

force is a vector quantity. in general F = F(x,t)

dx is a differential change in the position vector x.

so there is a dot product operator between F and dx -- that ensures work is a scalar quantity.

Note: W = Integral[ dW ]; so dW = F.dx

the idea is that the force can change along the path defined by x(t).

so in order to calculate the work done, one just have to sum up the differential contributions dW along the entire path.

summing differential contributions amounts to integration (via the line integral.)

the associated concept from math (integral calculus) is the Riemann sum, and how integration is the limit of the Riemann sum as the dissection interval goes to zero.