Python 3, 89 86 bytes

[*s],*L=input().split()
while L:a,b,*L=map(int,L);s[a],s[b]=s[b],s[a]
print(*s,sep="")

Unpack all the things. (3 bytes saved thanks to @potato)

CJam, 13 bytes

r[q~]2/{~e\}/

Test it here.

Explanation

r             e# Read the first token, i.e. the string.
 [q~]         e# Read the rest of the input, eval it and wrap it in an array.
     2/       e# Split the array into pairs of consecutive elements.
       {   }/ e# For each pair.
        ~     e# Unwrap the array.
         e\   e# Swap the corresponding elements in the string.

C (137 b)

f(char*T,int*V,int L){int C=0;for(int j=0;j<strlen(T);C=++j){for(int i=L-1;i+1;i--)if(C==V[i]){C=V[i-i%2*2+1];i-=i%2;}printf("%c",T[C]);}}

Explanation is coming ...

Arguments

T = a word of type char*.

V = an array of an even number of integer elements.

L = length of V

Output

mixed string

How does it work ?:

sweeps numbers of array V vice versa , and puts the nth element of the string after tracking all its progress until the actual point . Example

input= T="First" , V={1,2,1,0,0,4}

V inversed={4,0,0,1,2,1}

V[0] = 4th element -> index 0
0 -> 1
1->2

4th element 't' receives the second = 'r'

V[1] = 0 -> index 4
4 isnt mentionned after so , no changes

0 element='F' receives the fourth= 't'

V[3] = 1st element -> index 0
no changes

V[4] = 2 -> index 1
no changes after ..

Try it here

Python 3 - 161 149

import sys
t=sys.stdin.read().split()
q=list(t[0])
c=1
i=int
while c<len(t):n=q;a=i(t[c]);b=i(t[c+1]);n[a]=q[b];n[b]=q[a];q=n;c+=2;
print(''.join(q))

Golfed more by swapping around some variables, and using ; as in Tim's comment.

I expected it to come out looking golfed, just not this much.

C, 109 107 102 bytes

i;f(l){l=sizeof(a)/sizeof(*a);char t;for(;i<l;i+=2){t=s[a[i]];s[a[i]]=s[a[i+1]];s[a[i+1]]=t;}puts(s);}

Note: s and a needs to be declared as global arrays. s is the string which you want to swap and a is an array of int with all the number values.

If the above code does not work, try using void f(){...} instead of f(){...}

Ungolfed code:

int a[]={1, 2, 1, 0, 0, 4};//Integer elements
char s[]="First";          //String to be swapped

i; //Auto initialized to 0 and defaults to type int
void f(l){ //Variables defaults to type int
  l=sizeof(a)/sizeof(*a); //Gets number of elements in array a
  char t;

  for(;i<l;i+=2){ 

    t=s[a[i]];
    s[a[i]]=s[a[i+1]];
    s[a[i+1]]=t;  //Swap each character

  }

  puts(s); //Print the final char array
}

Test it here

Python 3, 135

x=input().split()
y=list(x[0])
z=[int(i)for i in x[1:]]
while z:p,c=y[z[0]],y[z[1]];y[z[0]],y[z[1]]=c,p;del z[0],z[0]
print(''.join(y))

Explanation:

x=input().split()         # Split the input into a list at each space
y=list(x[0])              # First item in list (the word) into a list of chars
z=[int(i)for i in x[1:]]  # Make the list of numbers, into integers
while z:                  # Loop untill the list z is empty
    p,c=y[z[0]],y[z[1]]   # Assign p to the first char and c to the second
    y[z[0]],y[z[1]]=c,p   # Swap around using p and c
    del z[0],z[0]         # Remove the first 2 items in the list of integers
print(''.join(y))         # Print out the altered list as a string

C, 70 bytes

Given that the input string is at most length 100 I decided to make the 'NULL' byte indicating the end of the integer array be the unambiguous 0xFF. Presumably this doesn't count as extra input, though for a cost of (at most) 7 3 bytes it can be made into 1-based indexing and use '\0' as the end of the array.

f(s,i,t)char*s,*i;{for(;~*i;)t=s[*i],s[*i]=s[*++i],s[*i++]=t;puts(s);}

Pretty much just does regular swapping with a tmp variable and uses that the comma operator introduces sequence points to have defined behaviour (unlike some manifestations of xor swaps that would have a lower character count but lead to undefined behaviour).

Edit: As requested you can test it out: http://rextester.com/OVOQ23313.

Dart - 123

Assumes input on the command-line is automatically split at spaces. Otherwise it needs an initial x=x[0].split(' '); to split the string into text and indices.

main(x,{c,i:1,a,t}){c=x[0].split("");n()=>a=int.parse(x[i++]);for(;i<x.length;t=c[n()],c[a]=c[n()],c[a]=t);print(c.join());}

With more whitespace:

main(x,{c,i:1,a,t}){
  c=x[0].split("");
  n()=>a=int.parse(x[i++]);
  for(;i<x.length;t=c[n()],c[a]=c[n()],c[a]=t);
  print(c.join());
}

Run/test this on dartpad.dartlang.org.

Rebol - 71

s: take i: split input" "foreach[a b]i[swap at s do a at s do b]print s

Ungolfed:

s: take i: split input " " 
foreach [a b] i [swap at s do a at s do b]
print s

C, 143 bytes

main(a,v,i)char** v;{i=2;char s[101],t;strcpy(s,v[1]);for(;i<a;i+=2){t=s[atoi(v[i])];s[atoi(v[i])]=s[atoi(v[i+1])];s[atoi(v[i+1])]=t;}puts(s);}

The above program takes input from command-line arguments, copies the string into an array, swaps corresponding characters and then, outputs the modified string.

Ungolfed code:

main(int a,char** v,int i){ //Arguments of main 
  i = 2;
  char s[101],t;

  strcpy(s,v[1]); //Copy string literal into an array

  for(;i<a;i+=2){
    t=s[atoi(v[i])];
    s[atoi(v[i])]=s[atoi(v[i+1])];
    s[atoi(v[i+1])]=t;  //Swap each character
  }

  puts(s); // Output the final string
}