USE SOMETHING ELSE OPTION

0. ORIGINAL QUESTION
   
   First you need to identify if Windows 7 is installed in UEFI or legacy mode. You can easily do this via BIOS settings or from Windows. Run msinfo32.exe from Regedit, which can be opened with Windows + R. Under System Summary you can find BIOS MODE line with exact mode of installation.

   
   

   Now you can proceed with installation. Depending on your PC/laptop you need to boot USB as BIOS mode (often named LEGACY mode on newer PCs). Easiest option would be to disable UEFI boot in BIOS settings completely. You will not need it now, and if you ever need it, you can easily enable it again. That option is probably under BOOT section of BIOS settings (or something similar depending on manufacturer. Now when that part is completed, you can proceed with instructions.

   
   



1. Choose "Something else" on step 4 of Ubuntu install:

   
   

   

   
   



2. You will see your disk as /dev/sda,/dev/sdb and /dev/sdc. You said that you want
   to install it on /dev/sda, so choose that device and press - to delete
   existing partition on it(/dev/sda1) NOTE: Make sure that you want to delete
   that partition, and if it contains some important data make a backup. If you want to
   resize it, use change option and choose new size of /dev/sda1 so you can
   leave some room for other partitions.
   Click "New Partition Table..." Now you will see empty space for your Ubuntu
   installation:
   

   
   



3. Recommended if you are low on RAM Create swap partition, swap is the partition for
   keeping unneeded memory pages, like Windows swap. Also it can be used for
   hibernation. Note that swap is much slower compared to RAM, so too much swap can
   slower you system. Use following table for guidance:

   
   

     RAM   No hibernation    With Hibernation  Maximum
   
     1GB              1GB                 2GB      2GB
   
     2GB              1GB                 3GB      4GB
   
     3GB              2GB                 5GB      6GB
   
     4GB              2GB                 6GB      8GB
   
     5GB              2GB                 7GB     10GB
   
     6GB              2GB                 8GB     12GB
   
     8GB              3GB                11GB     16GB
   
    12GB              3GB                15GB     24GB
   
    16GB              4GB                20GB     32GB
   
    24GB              5GB                29GB     48GB
   
    32GB              6GB                38GB     64GB
   
    64GB              8GB                72GB    128GB
   
   128GB             11GB               139GB    256GB
   
   256GB             16GB               272GB    512GB
   
   512GB             23GB               535GB      1TB
   
     1TB             32GB              1056GB      2TB
   
     2TB             46GB              2094GB      4TB
   
     4TB             64GB              4160GB      8TB
   
     8TB             91GB              8283GB     16TB
   
   

   
   

SOURCE: https://help.ubuntu.com

• Select free space and click +


• Set parameters like on the picture below:
  

4. Create partition for / (root partition). This is base partition which contains Kernel, system files, program files etc. So like C partition on Windows. You need about 20GiB for this partition, but you put more (if you have space) and if you need more in some time, you can simply extend it via GParted live USB.So:

• Select free space and click +


• Set parameters like on the picture below:
  

5. Create /home partition. This is the partition for your user's files, like documents, images, song, movies etc. So like Users folder on on Windows.

   
   

   You can do this just like in step 4.

   
   



6. For advance users You can probably skip this part, but I will still put it here. Create separate /boot, /tmp and /var partitions. For exact sizes of partition use this:

   
   

• /boot 100 – 500 MiB


• /var and /tmp should be > 5 GiB
  or modify these values according to your needs.

After all that, you should see your disk like this:

P.S.
Also you asked about having separate / and /home partitions. Strictly speaking you don't need to. That is a question of personal taste, but having a separate /home partition would help you in case of errors during upgrade to new release of Ubuntu. There is always a small chance of some kind of error in system upgrade which can result in data loss.

That is it! You can now click on Install Now and start enjoying Ubuntu.