If erection is not strong enough... to wear a condom is more difficult:
1- Unroll half of the condom and put some fingers of your 2 hands in the lower part of the condom like in the photo
2-Try that your finger never touch the lower part of the condom.
3-The fingers must enlarge the lower part of the condom only
4-Attention! Don't touch the latex with your nails like in the following photo!
5-Fill the upper part of the condom with the head of the penis
6-Only the head of the penis should touch the upper part of the condom... Remember that the main target is to protect the head of the penis.
7-Fill the lower part of the condom with the weak penis...
8-...and try to reach the root of the penis.
9-Now you can start your intercourse.
10-...But do not forget to have light because the lower part of the condom is more susceptible to break after such manipulation.